feat(voyage): add lib/validators/profile-validator.mjs — SC #1, #2, #3

Step 5 av v4.1-execute (Wave 2, Session 2).

Profile-validator etter brief-validator-mønsteret eksakt: validateProfileContent
(pure), validateProfile (file-reader), CLI shim med --json flag. Eksporter
PROFILE_REQUIRED_FIELDS (frozen), PROFILE_REQUIRED_PHASES (frozen).

Validerer:
- Required frontmatter fields (name, phase_models, parallel_agents_min/max,
  external_research_enabled, brief_reviewer_iter_cap)
- phase_models = list-of-dicts med phase + model
- 6 required phases (brief, research, plan, execute, review, continue)
- parallel_agents_max ≥ parallel_agents_min
- Allowed model values: ['sonnet', 'opus']; haiku tillatt KUN ved
  VOYAGE_ALLOW_HAIKU=1 (per global CLAUDE.md modellvalg-prinsipp)

Issue codes: PROFILE_MISSING_FIELD, PROFILE_INVALID_MODEL, PROFILE_INVALID_ENUM,
PROFILE_READ_ERROR, PROFILE_NOT_FOUND.

Field-path-reporting i error-location: phase_models[N].model for SC #2.

Tester (10 nye, baseline 377 → 387):
- SC #1 x3 (innebygde profiler grønne)
- SC #2 (PROFILE_INVALID_MODEL med location phase_models[2].model)
- SC #3 (PROFILE_INVALID_ENUM for external_research_enabled: "yes" string)
- VOYAGE_ALLOW_HAIKU env-var deny/allow
- PROFILE_MISSING_FIELD når name fraværende
- PROFILE_NOT_FOUND for ikke-eksisterende fil
- 2 export drift-pins

Fixturer: profile-invalid-model.yaml (gpt-4 i phase_models[2]),
profile-invalid-enum.yaml (external_research_enabled som string "yes").

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/voyage/tests/fixtures/profile-invalid-enum.yaml

@@ -0,0 +1,21 @@
+---
+profile_version: "1.0"
+name: invalid-enum
+phase_models:
+  - phase: brief
+    model: sonnet
+  - phase: research
+    model: sonnet
+  - phase: plan
+    model: opus
+  - phase: execute
+    model: sonnet
+  - phase: review
+    model: opus
+  - phase: continue
+    model: sonnet
+parallel_agents_min: 4
+parallel_agents_max: 6
+external_research_enabled: "yes"
+brief_reviewer_iter_cap: 2
+---