feat: Morph Model Router as an opt-in complexity classifier (#68)

[doramirdor]

Closes #68.

Adds an optional, opt-in morph classifier that delegates the simple/mid/complex routing decision to Morph's hosted Model Router, built to the spec from the maintainer triage on #68.

What's in it

• New NADIRCLAW_COMPLEXITY_ANALYZER=morph — nadirclaw/morph_classifier.py with MorphRouterClassifier, wired into get_classifier() / warmup() dispatch alongside binary and distilbert.
• Strictly opt-in. Default stays the local binary classifier. morph requires MORPH_API_KEY; a missing key degrades to binary at selection time (never a hard dependency for first-run UX).
• Fail-closed to local. On missing key, HTTP error, timeout (>MORPH_TIMEOUT_MS, default 200ms), or an unparseable response, it logs once and serves that request from BinaryComplexityClassifier. A Morph outage degrades routing quality, never availability.
• Latency budget + cache. MORPH_TIMEOUT_MS bounds the call; a small in-memory LRU keyed on prompt hash absorbs the repeated prompts a CLI session generates.
• Consistent tiering. Morph's difficulty (easy/medium/hard/needs_info) maps to a complexity score, then to a tier via BinaryComplexityClassifier._score_to_tier, so the same NADIRCLAW_TIER_THRESHOLDS apply and mid only appears when NADIRCLAW_MID_MODEL is set.
• No new dependency. HTTP via stdlib urllib.request, so it's trivially monkeypatched.

Config knobs

Env var	Default	Purpose
MORPH_API_KEY	—	Required for morph; empty → fall back to binary.
MORPH_API_BASE	https://api.morphllm.com/v1	Self-hosted/proxy override.
MORPH_TIMEOUT_MS	200	Per-request budget; past it, fail closed.

Tests

tests/test_morph_classifier.py — 15 cases covering the success path, all three fail-closed paths (HTTP error, timeout, bad JSON), response parsing (confidence vs 1 − ambiguity, nested classification, bad/unknown difficulty), caching, and the dispatch/degrade-without-key behavior. No live API call — the HTTP layer is monkeypatched. Full suite: 812 passed, 1 skipped locally.

Deferred (called out in the README)

The maintainer asked for cost-tracking honesty — subtracting the per-classification Morph fee from net saved in nadirclaw report. Morph's classification price isn't published in the issue, so that wiring is left as a follow-up and noted in the docs rather than guessed at.

Notes for review

• The maintainer's triage suggested the env name NADIRCLAW_CLASSIFIER; the actual dispatch var in the codebase is NADIRCLAW_COMPLEXITY_ANALYZER, so I used that for consistency with binary/distilbert.
• Morph's exact response schema isn't pinned in the issue, so _parse_response is defensive (flat or nested under classification; confidence else 1 − ambiguity else 1.0) and any surprise falls through the fail-closed path.

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