docs(governance): record PoC outcomes, owner decisions, and audit evidence

Closes Phases A and D of the post-PoC sequencing.

Decision register (v0.9.2 → v0.9.3):
  - DEC-014 Accepted: flutter_rust_bridge 2.x pinned (closed by
    poc/flutter_rust_bridge_hello).
  - DEC-013.1 Accepted: rusqlite (bundled) (closed by
    poc/sqlite-storage-spike).
  - DEC-013.2 Accepted: Linux secure-storage backend policy —
    Secret Service preferred, keyutils fallback (closed by
    poc/secure-storage-spike; resolves SysRS-053 / SysRS-162
    ambiguity).
  - DEC-011.1 Accepted (desktop: cpal) / Deferred (mobile)
    (closed by poc/audio-capture-playback-spike desktop half only).
  - DEC-022 Accepted: canonical implementation directory layout per
    the README sketch and SAD §7.2.
  - DEC-020 explicitly Deferred by owner; remains a public-release
    blocker.

Audit reports updated with empirical evidence:
  - docs/security/secure-storage-audit-report.md v0.9.3:
    SS-AUD-001/002/003/005/006 = PoC Pass with evidence pointers;
    SS-TC-003 (Linux) Actual Result populated and Status = PoC Pass;
    SS-AUD-004 cross-referenced to diagnostics-redaction PoC;
    findings SS-FIND-001 (closed by DEC-013.2), SS-FIND-002 (keyutils
    session caveat), SS-FIND-003 (non-Linux adapters still open).
  - docs/security/diagnostic-redaction-audit-report.md v0.9.3:
    REDACT-TC-001..010 = PoC Pass with evidence pointers; export
    bundle policy §5 populated for every row; findings
    REDACT-FIND-001 (regex coverage), REDACT-FIND-002
    (tracing-layer integration), REDACT-FIND-003 (cross-spike
    KnownSecretRegistry contract).

PoC plan (v0.1.0 → v0.2.0):
  - Status column added to §2; outcomes recorded.

New doc:
  - docs/governance/poc-results-summary.md v0.1.0 — single-page
    reviewer-facing summary listing each spike's status, the
    toolchain exercised, the owner decisions taken, the audit
    coverage table, and open risks RISK-PoC-001..005 (mobile audio,
    non-Linux secure-storage adapters, license, remaining
    Proposed decisions, no product code yet).

This completes the post-PoC documentation work. Repo is at a clean
pause point: PoC code is committed, owner decisions are recorded,
audit reports carry empirical evidence, and the residual risks are
named in the summary doc.

CHANGELOG.md

@@ -39,7 +39,32 @@ This project is expected to follow a Conventional Commits style workflow.
 
 ### Changed
 
-- N/A
+- `docs/architecture/proof-of-concept-plan.md` bumped to v0.2.0 to
+  record PoC outcomes (5 PASS, 1 PARTIAL) and add a Status column.
+- `docs/security/secure-storage-audit-report.md` bumped to v0.9.3:
+  SS-AUD-001/002/003/005/006 status set to PoC Pass with evidence
+  pointers; SS-TC-003 (Linux) Actual Result populated and Status set
+  to PoC Pass; findings SS-FIND-001..003 added; non-Linux test cases
+  marked Deferred.
+- `docs/security/diagnostic-redaction-audit-report.md` bumped to
+  v0.9.3: REDACT-TC-001..010 status set to PoC Pass with evidence
+  pointers; export bundle policy §5 populated; findings
+  REDACT-FIND-001..003 added.
+- `docs/governance/product-decision-register.md` bumped to v0.9.3:
+  owner-confirmed decisions recorded — DEC-014 Accepted
+  (`flutter_rust_bridge` 2.x pinned), DEC-013.1 Accepted (`rusqlite`
+  bundled), DEC-013.2 Accepted (Linux Secret Service preferred,
+  keyutils fallback), DEC-011.1 Accepted (desktop `cpal`) / Deferred
+  (mobile), DEC-022 Accepted (canonical implementation directory
+  layout per README sketch + SAD §7.2), DEC-020 explicitly Deferred
+  and remains a public-release blocker.
+
+### Added (governance)
+
+- `docs/governance/poc-results-summary.md` v0.1.0 — single-page
+  reviewer-facing summary of the PoC phase, the toolchain exercised,
+  the owner decisions taken, the audit coverage, and the open risks
+  RISK-PoC-001..005.
 
 ### Fixed