Implement WP-0015-T01/T04/T06: Phase provenance schema + ledger UI

Schema: phase.milestone_release gains required repo_hub/repo_hub_uri/
repo_id/repo_name; phase gains optional base_phase_id. Backfilled the
golden phase-001 fixture (placeholder values, it's synthetic) and the
three real pilot-candidate manifests with actual Forgejo repo ids
confirmed live (net-kingdom=67, vergabe-teilnahme=62,
info-tech-canon=47, all coulomb/*).

Discovered along the way: the schema change alone would have broken
the existing Control Plane registration form, since nothing collected
the four new fields. Fixed inline rather than leaving it broken
between tasks -- this also completes T04's ledger UI change (drop the
hand-typed ledger input, auto-compute /phases/{id}/ledger, add a
drill-down reference link on phase_detail.html) since both changes
touch the same form/route.

Full suite: 94 passing offline (was 84), 158 passing with Docker
(was 146).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/phase-001/manifest.json

@@ -6,7 +6,11 @@
     "milestone_release": {
       "name": "release-1.0",
       "source_revision": "abc123",
-      "artifact_sha256": "44cd1493bd179c1207c7025c1372cdad89aac114e151db27aba2bdf3d55c688a"
+      "artifact_sha256": "44cd1493bd179c1207c7025c1372cdad89aac114e151db27aba2bdf3d55c688a",
+      "repo_hub": "example-hub",
+      "repo_hub_uri": "https://example.invalid",
+      "repo_id": 1,
+      "repo_name": "example/example-repo"
     },
     "initial_target": {
       "amount": 100000,