fix(db): handle readonly database gracefully instead of crashing (#235)

## Summary

When the CLI's local database (`~/.sentry/cli.db`) is on a read-only
filesystem or has wrong permissions, DB writes throw `SQLiteError:
attempt to write a readonly database` and crash commands. Now the CLI
catches these errors centrally in the traced DB proxy, warns the user
once, and continues working — reads still succeed, only
caching/persistence is lost.

Closes https://sentry.sentry.io/issues/7258516238/

## Changes

Readonly errors are caught in the traced DB proxy
(`createTracedStatement`) alongside the existing schema auto-repair
logic. A one-time warning prints to stderr pointing users to `sentry cli
fix`. This single change protects all ~14 DB write paths without
touching individual modules.

`sentry cli fix` now also checks file permissions on the DB file,
WAL/SHM journals, and config directory — and repairs them with `chmod`
when possible.

## Test Plan

- `bun run typecheck` — clean
- `bun run lint` — clean
- 88 tests pass across the 3 changed test files (schema, telemetry, fix
command)
- New tests: `isReadonlyError()` detection (5 cases), readonly proxy
behavior (4 cases: no throw on write, reads work, warns once, message
content)

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Co-authored-by: Burak Yigit Kaya <byk@sentry.io>

Author: betegon