fix(#2009): load-failed capability gates fail open with a loud warning

Previously a capability that failed to LOAD (e.g. incompatible engines.gsd) but
declared a gate-kind loop hook caused the loop resolver to inject a BLOCKING
synthetic gate (blocking:true, onError:halt) at every declared point, halting
every ship:pre / verify:post project-wide over an unrelated load error, with no
remediation surfaced.

Per maintainer decision (#2009) it now fails OPEN: no gate is injected (the loop
proceeds; --active-cap correctly reports the failed cap inactive) and a loud
warning is emitted — to stderr (the channel host workflows/agents actually see)
and in the envelope 'warnings' array — naming the load reason and the exact
'gsd capability remove <id>' remediation. The loader still records blockedGates;
only the consequence changes from block to warn.

Security (review): capId and reason originate from a third-party manifest /
directory name. capId is validated against the canonical kebab-case id shape
before it is placed in the runnable remediation command (withheld otherwise);
reason is stripped of control chars and backticks. This closes an argument/
prompt-injection vector in the surfaced message.

Docs updated to the fail-open-warning posture (ARCHITECTURE, INVENTORY,
CONFIGURATION, README, capability-overlay-model). Also removes a dead 'before'
import surfaced by lint in the issue-2045 test.

docs/README.md

@@ -72,7 +72,7 @@ Language versions: [English](README.md) · [Português (pt-BR)](pt-BR/README.md)
 - [Multi-agent orchestration](explanation/multi-agent-orchestration.md) — how subagents are spawned, scoped, and coordinated
 - [Security model](explanation/security-model.md) — trust boundaries, permissions, and safe automation
 - [The capability trust model](explanation/capability-trust-model.md) — why third-party capabilities are gated by consent + integrity + reversibility, not a sandbox
-- [How overlay capabilities compose](explanation/capability-overlay-model.md) — why first-party always wins and how the loader resolves precedence, conflicts, and fail-closed gates
+- [How overlay capabilities compose](explanation/capability-overlay-model.md) — why first-party always wins and how the loader resolves precedence, conflicts, and fail-open load-failure warnings
 - [Architecture](ARCHITECTURE.md) — system architecture, agent model, and data flow
 - [Discuss modes](workflow-discuss-mode.md) — assumptions mode vs interview mode for `/gsd-discuss-phase`
 - [Context monitoring](context-monitor.md) — context window monitoring hook architecture