feat(frame): add premise-validity gate (success/failure/simplest_alternative)

[MickaelV0]

Summary

• Adds Step 1b to `/frame` — a hard gate between interview and tier classification
• Three required fields: `success_in_6mo`, `failure_in_6mo` (must be falsifiable), `simplest_alternative` (with mandatory why-not)
• Frame artifact gains a Premise Validity section with all four sub-fields
• Non-falsifiable `failure_in_6mo` triggers a re-ask loop; proxy-metric failure modes surface an explicit Reframe | Abort prompt
• Version bump: `0.2.0 → 0.3.0`

Originating case: Roxabi/lyra#1162 — quality-debt annotation infrastructure (~1100 LOC + 6 registry files) where `failure_in_6mo` would have been "DEBT count stays flat despite 3 sprint cycles" and `simplest_alternative` would have pointed directly to a regression-cap ratchet (~130 LOC, ~95% of the value).

Closes #169

Acceptance checklist

• Concrete change to `dev-core:frame` skill
• Quality-debt invariant: POLICY/DEBT tag grammar + audit + ratchet gate (P0+P1) lyra#1162 referenced as originating example in SKILL.md Step 1b
• All 3 fields required (block progression to Step 2)
• `failure_in_6mo` falsifiability enforced with re-ask + abort signal
• Frame artifact template updated with required Premise Validity section
• README updated (step numbering, output fields)
• lint pass | typecheck pass | 507 tests pass
• Out of scope: `global-patterns.md` documentation — follow-up needed (file is `~/.claude/shared/global-patterns.md`, out-of-tree for this repo; requires a separate cross-repo update)

Coupling note

Issue #168 (`/plan` budget heuristic) is in-flight in parallel. Neither branch touches the same files — no conflict expected.

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