[cli] Make all short names upper cases + Enable pipe mode and file mode (#203)

This PR updates the Decimo CLI to avoid short-flag collisions with
negative expressions by uppercasing short options, and adds new stdin
(pipe) + file-based input modes for evaluating multiple expressions.

**Changes:**
- Uppercase short flags for formatting/computation options
(`-P/-S/-E/-D/-R`) and remove the `--pad` short flag to prevent
collisions with expressions like `-e`, `-pi`, `-sin(1)`.
- Add pipe mode (read/evaluate expressions from stdin, one per non-empty
non-comment line) and file mode (`-F/--file`).
- Extend integration/unit tests and update docs/changelog/plans for the
new CLI UX.

Author: forfudan

docs/changelog.md

@@ -2,6 +2,17 @@
 
 This is a list of changes for the Decimo package (formerly DeciMojo).
 
+## Unreleased - under development
+
+### ⭐️ New in v0.10.0
+
+**CLI Calculator:**
+
+1. Add **pipe/stdin mode**: read expressions from standard input, one per line, when no positional argument is given and stdin is piped (e.g. `echo "1+2" | decimo`, `printf "pi\nsqrt(2)" | decimo -P 100`). Blank lines and comment lines (starting with `#`) are automatically skipped.
+1. Add **file mode**: use `--file` / `-F` flag to evaluate expressions from a file, one per line (e.g. `decimo -F expressions.dm -P 50`). Comments (`#`), inline comments, and blank lines are skipped. All CLI flags (precision, formatting, rounding) apply to every expression.
+
+### 🦋 Changed in v0.10.0
+
 ## 20260323 (v0.9.0)
 
 Decimo v0.9.0 updates the codebase to **Mojo v0.26.2** and marks the **"make it useful"** phase. This release introduces three major additions:

docs/plans/cli_calculator.md

@@ -95,7 +95,7 @@ cat expressions.txt | decimo
 decimo < expressions.txt
 
 # Evaluate a script file (.dm)
-decimo file.dm
+decimo -F file.dm
 ```
 
 Example `expressions.dm`:
@@ -266,17 +266,17 @@ Format the final `BigDecimal` result based on CLI flags:
 6. Handle unary minus.
 7. Test with basic expressions.
 
-| #   | Task                                             | Status | Notes                         |
-| --- | ------------------------------------------------ | :----: | ----------------------------- |
-| 1.1 | Project structure (src/cli/, calculator module)  |   ✓    |                               |
-| 1.2 | Tokenizer (numbers, `+ - * /`, parens)           |   ✓    |                               |
-| 1.3 | Shunting-yard parser (infix → RPN)               |   ✓    |                               |
-| 1.4 | RPN evaluator using `BigDecimal`                 |   ✓    |                               |
-| 1.5 | ArgMojo wiring (`expr`, `--precision`, `--help`) |   ✓    |                               |
-| 1.6 | Unary minus                                      |   ✓    |                               |
-| 1.7 | Basic expression tests                           |   ✓    | 4 test files, 118 tests total |
-| 1.8 | Pipeline / stdin input (`echo "1+2" \| decimo`)  |   ✗    | Not yet implemented           |
-| 1.9 | File input (`decimo file.dm`)                    |   ✗    | Not yet implemented           |
+| #   | Task                                             | Status | Notes                                                                                        |
+| --- | ------------------------------------------------ | :----: | -------------------------------------------------------------------------------------------- |
+| 1.1 | Project structure (src/cli/, calculator module)  |   ✓    |                                                                                              |
+| 1.2 | Tokenizer (numbers, `+ - * /`, parens)           |   ✓    |                                                                                              |
+| 1.3 | Shunting-yard parser (infix → RPN)               |   ✓    |                                                                                              |
+| 1.4 | RPN evaluator using `BigDecimal`                 |   ✓    |                                                                                              |
+| 1.5 | ArgMojo wiring (`expr`, `--precision`, `--help`) |   ✓    |                                                                                              |
+| 1.6 | Unary minus                                      |   ✓    |                                                                                              |
+| 1.7 | Basic expression tests                           |   ✓    | 4 test files                                                                                 |
+| 1.8 | Pipeline / stdin input (`echo "1+2" \| decimo`)  |   ✓    | Pipe mode: reads stdin when no positional arg and stdin is not a TTY                         |
+| 1.9 | File input (`decimo -F file.dm`)                 |   ✓    | File mode via `-F/--file` flag: reads files line by line, skips comments (#) and blank lines |
 
 ### Phase 2: Power and Functions
 
@@ -328,7 +328,7 @@ Format the final `BigDecimal` result based on CLI flags:
 | 3.13 | Documentation (user manual for CLI)                             |   ✗    | `docs/user_manual_cli.md`; include shell completion setup                                  |
 | 3.14 | Build and distribute as single binary                           |   ✗    |                                                                                            |
 | 3.15 | Allow negative expressions                                      |   ✓    | `allow_hyphen=True` on `Positional`; `decimo "-3*pi*(sin(1))"` works                       |
-| 3.16 | Make short names upper cases to avoid expression collisions     |   ✗    | `-sin(1)` clashes with `-s` (scientific), `-e` clashes with `--engineering`                |
+| 3.16 | Make short names upper cases to avoid expression collisions     |   ✓    | `-P`, `-S`, `-E`, `-D`, `-R`; `--pad` has no short name; `-e`, `-pi`, `-sin(1)` all work   |
 | 3.17 | Define `allow_hyphen_values` in declarative API                 |   ✗    | When argmojo supports it                                                                   |
 
 ### Phase 4: Interactive REPL & Subcommands
@@ -408,7 +408,7 @@ This is the natural choice for a calculator: users expect `7 / 2` to be `3.5`, n
 | ------------------------------------- | ------------------------------------- |
 | `decimo "expr"`                       | One-shot: evaluate and exit           |
 | `echo "expr" \| decimo`               | Pipe: read stdin line by line         |
-| `decimo file.dm`                      | File: read and evaluate each line     |
+| `decimo -F file.dm`                   | File: read and evaluate each line     |
 | `decimo` (no args, terminal is a TTY) | REPL: interactive session             |
 | `decimo -i`                           | REPL: force interactive even if piped |