taxis: smart path sanitization

[forkwright]

Context

`crates/taxis/src/import/template.rs::sanitize_path_segment` currently replaces all of `/ \ : * ? " < > |` with ``. This produces ugly results: `Title: Subtitle` becomes `Title Subtitle`, double-spaced. The canonical layout uses smart per-character rules.

What

Replace the `UNSAFE` constant + the simple character substitution with a per-character smart rule table:

Char	Replacement	Rationale
`:`	` -` (space-dash)	`Title: Subtitle` → `Title - Subtitle`
`/`	`-`	Slash separator
`\`	`-`	Same as forward slash
`|`	`-`	Pipe separator
`*`	(removed)	Glob char
`?`	(removed)	Glob char
`<`	(removed)	Redirection
`>`	(removed)	Redirection
`"`	(removed)	Quote
`'` (curly U+2018, U+2019)	`'` (straight)	Grep consistency
`"` (curly U+201C, U+201D)	`"` (straight)	Grep consistency

After substitution, collapse whitespace runs to a single space and trim. UTF-8 unicode is preserved (Björk, $uicideboy$, ñ, é all keep their characters).

Files

• `crates/taxis/src/import/template.rs` — `sanitize_path_segment` function + tests

Acceptance

• `sanitize_path_segment("Title: Subtitle")` returns `"Title - Subtitle"`
• `sanitize_path_segment("AC/DC")` returns `"AC-DC"`
• `sanitize_path_segment("What's Up?")` returns `"What's Up"` (curly apostrophe normalized, question mark removed)
• `sanitize_path_segment("Björk")` returns `"Björk"` (unicode preserved)
• `sanitize_path_segment("$uicideboy$")` returns `"$uicideboy$"` (dollar signs preserved)
• Existing tests updated to assert smart replacements instead of underscore

Reference

Migration plan: 2026-04-09 chat session. Reference implementation in the migration scripts: `~/menos-ops/scratch/migrate-music-canonical.py` (`clean_name` function).