feat(triggers): runtime mute config for SKILL_OBSERVATION_TRIGGER

[AVADSA25]

Summary

• Adds ~/.codec/triggers.json runtime config so users can soft-disable a trigger by skill name without editing the skill file. Two knobs: muted_skills (permanent) and muted_until (ISO-8601 timestamp).
• New trigger_muted audit event (warning level) — muted-but-otherwise-eligible matches stay visible in the log, unlike the silent triggers_killed.json kill switch.
• Restores clipboard_url_fetch.SKILL_OBSERVATION_TRIGGER (uncommented). Old PR hotfix: stop trigger + shift_report notification spam #38 behavior is preserved by config defaults ({"muted_skills": ["clipboard_url_fetch"]} when the file is absent), not by commented-out code.

Why

PR #38 muted the noisy clipboard URL trigger by commenting out its SKILL_OBSERVATION_TRIGGER block. That works but:

• requires editing the skill file,
• can't be re-enabled per user,
• loses the declaration entirely.

The existing per-(skill, pattern_hash) kill switch in triggers_killed.json is silent (no audit emit), and TRIGGERS_ENABLED=false is a global sledgehammer. This PR adds a per-skill, audit-visible suppression layer — see docs/PHASE2-STEP6-TRIGGER-MUTE.md §6 for the kill-vs-mute comparison table.

Wiring

In evaluate(), mute is checked between _emit_evaluated() and the cooldown check. Muted matches do not consume cooldown budget, do not trigger trigger_blocked: cooldown emits, and do not invoke the consent gate. They emit a single trigger_muted event with mute_source ∈ {muted_skills, muted_until}.

Tests

3 new in tests/test_triggers.py §7.6:

• test_muted_skill_name_skips_fire — full integration through evaluate(), asserts no dispatch + trigger_muted audit emit
• test_muted_until_past_timestamp_not_muted — expired timestamps don't mute
• test_muted_until_future_timestamp_muted — future timestamps mute

Result: 38/38 trigger tests pass (35 baseline + 3 new). All other test failures are pre-existing on main (pynput import, see docs/known-issues.md).

Test plan

• pytest tests/test_triggers.py — 38/38 pass
• pytest tests/test_clipboard_url_fetch.py — 14/14 pass (1 pre-existing pynput-import failure)
• pytest tests/test_observer.py — passes
• Confirmed test_destructive_consent::test_is_destructive_tool_triggers_on_http_blocked failure is pre-existing on baseline (verified via git stash)
• Reviewer to spot-check: drop a fresh ~/.codec/triggers.json with {"muted_skills": []}, restart codec-observer, copy a URL → confirm clipboard_url_fetch now auto-fires (verifies file overrides defaults)
• Reviewer to spot-check: tail ~/.codec/audit.log while triggering a clipboard pattern → confirm one trigger_muted warning emitted with mute_source: "muted_skills"

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