feat(threats): author-controlled manual ids, Critical priority, and register origin/status

[Hacks4Snacks]

feat(threats): author-controlled manual ids, Critical priority, and register origin/status

Implements THR-002. The threat register now has a stable public contract: authors own
manual ids and priority, and every surface distinguishes manual, current-generated,
persisted-generated, and stale entries.

What changed

Stable manual identity. ManualThreatId (Core) is the single definition of the
reserved manual: namespace. threats --add --id, AuthoringService.AddThreat, and the
MCP add_threat tool accept an author-supplied id, canonicalize it (prefix optional,
[A-Za-z0-9._-], 1–128 chars), and refuse a duplicate rather than overwriting the
existing threat's triage.

Critical priority, tmforge-wide. ThreatPriority is the one vocabulary and
ThreatPriorities canonicalizes it for every surface. Severity→priority defaults are
unchanged, so no existing threat moved. The embedded knowledge base now declares the whole
vocabulary with IsPriorityUsed; at a foreign KB the two vocabularies are unioned, so
neither side's values become unselectable.

Register origin/status. ThreatRegisterClassifier splits the register against one
generation run. Staleness is only claimed when the rule was present and enabled and still
did not fire; a rule absent or disabled is reported as indeterminate with the rule named,
never assumed stale.

Stale entries are inspectable and removable. list threats shows a STANDING column;
threats --remove-stale clears leftovers. A stale entry carrying triage is kept and named
— --force is the explicit way to discard it — and pruning refuses outright when any
entry's rule was not part of the run.

Surfaces: open --json + human output, list threats, HTML report (stale badge),
POST /v1/model/threat-register, WASM ThreatRegister, MCP threat_register. The engine
projection rides the existing single-evaluation seam (AnalysisProjection.Register), so it
costs no extra rule run.

Behavior changes

• Exported .tm7 bytes change: the embedded KB now declares IsPriorityUsed and the
  priority value list.
• convert --knowledge-base output changes (it is now prepared like every other tm7 write).
• threats --remove <id> accepts a stale entry; a threat the rules still produce is still
  refused.
• openapi/v1.json and Studio schema.d.ts regenerated.