docs: Update documentation to reflect status spine output format

[konard]

Summary

Updates all documentation to correctly reflect the new "status spine" output format introduced in PR #65.

Changes

README.md

• Updated "Automatic Logging" section with spine format example
• Updated "Auto-Reporting on Failure" section with spine format example
• Updated "Log File Format" section with spine format example
• Added explanation of format conventions (│, $, ✓/✗ prefixes)

ARCHITECTURE.md

• Updated "Logging Architecture" section with new console output format
• Added format key explaining prefixes and markers

REQUIREMENTS.md

• Updated "Output Format" section with spine format examples
• Added format conventions documentation
• Updated Success, Failure with Auto-Reporting, and Failure without Auto-Reporting examples

Format Overview

The new "status spine" format:

│ session   abc-123-def-456-ghi
│ start     2024-01-15 10:30:45
│
$ command

... output ...

✓
│ finish    2024-01-15 10:30:52
│ duration  7.456s
│ exit      0
│
│ log       /tmp/start-command-123.log
│ session   abc-123-def-456-ghi

Format key:

• │ prefix → tool metadata
• $ prefix → executed command
• No prefix → program output (stdout/stderr)
• ✓ / ✗ → result marker (success/failure)

Test Plan

• All existing tests pass (bun test)
• Linting passes (bun run lint)
• Documentation examples are consistent with actual code behavior
• Case studies (historical documentation) preserved unchanged

Fixes #66

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[konard]

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