feat: target AKM 0.9.6

[itlackey]

Summary

• raise the shared compatibility floor and bundled dependency to AKM 0.9.6
• model the additive search matchStage contract
• update fixtures, tests, and user-facing install guidance

Validation

• 285 Bun tests
• Claude and OpenCode typechecks
• real AKM 0.9.6 envelope contract checks
• Tier 2 eval baseline: no regressions
• Tier 3 stub smoke

[github-actions]

Eval diff

• Baseline SHA: 83de80205da91f6789ffeb9b063f8b89ed91f730
• Candidate SHA: 62eaa78f0c9c16c288961853b3dc969a91e47a5d

Metric deltas

Metric	Key	Baseline	Candidate	Δ	Δ%	Status
curation	mean_expected_coverage	0.9125	0.9125	0	0.00%	• unchanged
curation	mean_reciprocal_rank	0.9208	0.9208	0	0.00%	• unchanged
curation	zero_hit_rate	0.0500	0.0500	0	0.00%	• unchanged
context_budget	claude_violations	0	0	0	0.00%	• unchanged
context_budget	opencode_violations	0	0	0	0.00%	• unchanged
context_budget	claude_drop_rate	0	0	0	0.00%	• unchanged
context_budget	opencode_drop_rate	0	0	0	0.00%	• unchanged
feedback	claude_precision	1	1	0	0.00%	• unchanged
feedback	claude_recall	1	1	0	0.00%	• unchanged
feedback	claude_polarity_flips	0	0	0	0.00%	• unchanged
feedback	opencode_precision	1	1	0	0.00%	• unchanged
feedback	opencode_recall	1	1	0	0.00%	• unchanged
feedback	opencode_polarity_flips	0	0	0	0.00%	• unchanged

Plugin surface

No surface changes.

No regressions.