feat(persona): fuzzy --theme/--persona resolution + 'persona list <theme>'

[arcaven]

Summary

Replaces exact-slug-only lookup with a three-tier match: exact → unique case-insensitive prefix → fuzzy subsequence (via nucleo-matcher, Helix editor's matcher). Makes the ~100 themes + ~1050 characters accessible without memorising canonical slugs.

Depends on #58 (legacy role retired — merged).

Design (session-032)

Resolution order (match_slug):

1. Exact slug (case-insensitive) — always wins.
2. Unique prefix — kubectl-style partial ID (disc → discworld).
3. Fuzzy subsequence with two thresholds:
   • >= MIN_FUZZY_SCORE AND gap >= FUZZY_AMBIGUITY_GAP vs rank-2 → FuzzyUnique
   • >= MIN_FUZZY_SCORE but tight with rank-2 → FuzzyAmbiguous (proceed with top, warn on stderr with candidates)
   • below MIN_FUZZY_SCORE → NotFound (caller errors, shows candidates)

Two-phase resolver (resolve_theme_and_persona):

• Resolve --theme first. When it succeeds, narrow --persona matching to that theme's ~10 characters. ~100× fewer candidates drops ambiguity to near-zero.
• If --theme is missing or unresolvable and --persona is given, search characters globally and back-propagate the matched character's home theme. stderr warning names the override.

What users can now type

Input	Resolves to
--theme disc --persona grny	discworld + granny-weatherwax
--theme discworld --persona lhv	discworld + lord-havelock-vetinari (initials)
--persona granny-weatherwax (no theme)	discworld + granny-weatherwax (back-prop)
--persona mvl	discworld + moist-von-lipwig
persona list disc	discworld's 11-character roster
persona show disc --agent ponder	ponder-stibbons card

New

• src/resolve.rs — MatchResult<T> enum, match_slug, match_theme, match_character_in_theme, match_character_globally, resolve_theme_and_persona. 15 unit tests.
• persona list <theme> subcommand — lists characters in a theme with slug + name + one-line style. Without arg, lists themes (unchanged).
• nucleo-matcher v0.3.1 — ~200KB, pure Rust, no C deps.

Wired into

• Top-level CLI flags (--theme, --persona): resolved before cli_overrides build, so config merge sees canonical slugs only.
• persona show <theme> — theme slug fuzzy-resolved.
• persona show <theme> --agent <slug> — character slug fuzzy-resolved within theme roster.
• persona list <theme> — theme slug fuzzy-resolved.

Test plan

• cargo test --release --lib — 150 pass (132 pre-existing + 3 from PR 58 + 15 new)
• cargo clippy --release --all-targets -- -D warnings — clean
• cargo build --release — clean
• Manual: persona list disc → shows discworld roster
• Manual: persona show disc --agent grny → Granny's card
• Manual: persona show disc --agent lhv → Vetinari (initials)
• Manual: --theme disc --persona grny config → theme = "discworld", character = "granny-weatherwax"
• Manual: --persona al --theme 1984 (no match) → stderr warning + hard error with candidates
• Manual: persona show xxx → hard error with hint (theme subcommand doesn't back-prop — design choice, only top-level CLI does)

Known behavior worth naming

• Short queries that don't score above MIN_FUZZY_SCORE (e.g. dw against a 5-theme pool) return NotFound rather than a weak match. Users can be more specific or use persona list to browse.
• Cross-theme name collisions surface via the ambiguity warning. Example: --persona starbuck resolves to Moby Dick's Starbuck (exact slug match) rather than Battlestar Galactica's Kara Thrace (whose slug is kara-starbuck-thrace). This is the B14 "persona = character slug" model doing its job.

Refs

• bd: aae-orc-jwqz (P2 feature)
• Follows PR 57 + PR 58 from session-032.