feat(P1): remove gitea/gitlab from synced files + simplify docs (REQ-230,231,232)

Genericize forge-detection code: gitea→forge/generic_forge, GITEA_ACTOR→FORGE_ACTOR.
Drop .gitea byte-identity test assertions (keep GitHub-side + contract conformance).
Add test_no_forge_mentions.py guard test (REQ-230).
Delete completed migration docs (NOVA_MIGRATION.md, NOVA_AWS_MIGRATION.md).
Move NO_HUMANS_THESIS.md to .ciagent/ (internal artifact).
Strip ciagent-internal provenance from synced docs (REQ-/D-/P-/CAP- IDs,
milestone headers, .ciagent/PROJECT.md citations).
Trim README.md (reusable deploy section, local key rotation paragraph).
Fix version-tag drift (@v1.13→@v1.19, acdl/→nova/).

---ci---
project: acdl
phase: 1
milestone: v1.20
status: execute
requirements: [REQ-230, REQ-231, REQ-232]
---/ci---

scripts/run_ci.sh

@@ -2,7 +2,7 @@
 # scripts/run_ci.sh - reproduce the CI pipeline locally.
 #
 # Mirrors the central pipeline contract (pipelines/ci.yml) which both
-# .gitea/workflows/ci.yml (Gitea Actions, dev) and
+# .github/workflows/ci.yml (dev) and
 # .github/workflows/ci.yml (GitHub Actions, production) implement.
 #
 # Runs the same three stages in the same order:

scripts/run_platform.sh

@@ -163,9 +163,9 @@ run_hitl_gate() {
     return 0
   fi
   echo "Environment is $_env — HITL attestation gate required$_ctx."
-  local _approver="${GITHUB_ACTOR:-${GITEA_ACTOR:-}}"
+  local _approver="${GITHUB_ACTOR:-${FORGE_ACTOR:-}}"
   if [ -z "$_approver" ]; then
-    echo "WARNING: no approver identity (GITHUB_ACTOR/GITEA_ACTOR unset)" >&2
+    echo "WARNING: no approver identity (GITHUB_ACTOR/FORGE_ACTOR unset)" >&2
     echo "         the gate would block in a real CI run. Passing for local." >&2
   fi
   python3 -c "