fix: harden forge command prompt against DCP context compression

[jflowers]

Summary

Restructures the /forge command prompt (internal/agentkit/content/commands/forge.md) to survive DCP context compression, fixing the quality gate vulnerability where the review-before-complete ordering constraint was lost under compression.

Addresses all four fragilities identified in #47:

1. Review-before-complete ordering embedded with explicit constraint language
2. Critical review rule moved from 5th to 1st position
3. Error Recovery section inlined at point of use
4. Strategy Selection section inlined at point of use

Additionally documents the skip_review: true API bypass discovered during spec review and adds a prohibition to the Critical Invariants section.

How to Test

# Build succeeds (forge.md is embedded content)
make build

# All tests pass (no behavioral changes)
make test

# Verify all 17 MCP tool references preserved
grep -c 'forge_review\|forge_complete\|comms_inbox\|forge_status' \
  internal/agentkit/content/commands/forge.md

# Verify review constraint in 3 redundant locations
grep -n 'review.*before.*complete\|MUST finish before step 8\|NEVER skip' \
  internal/agentkit/content/commands/forge.md

How to Demo

Read internal/agentkit/content/commands/forge.md and verify the restructured prompt:

• Critical Invariants section appears before Workflow
• Step 7 includes "MUST finish before step 8"
• First rule in Rules section is the review-before-complete rule
• No standalone Strategy Selection, Error Recovery, or Completion sections remain

Key Files Changed

File	Change
internal/agentkit/content/commands/forge.md	Restructured for DCP compression resilience (+22/-39 lines)
openspec/changes/forge-dcp-hardening/proposal.md	Change proposal with constitution alignment
openspec/changes/forge-dcp-hardening/design.md	6 design decisions with risk analysis
openspec/changes/forge-dcp-hardening/specs/forge-prompt-structure.md	Delta spec with Given/When/Then scenarios
openspec/changes/forge-dcp-hardening/tasks.md	Implementation tasks (all complete)

This PR was generated by /uf.finale (AI-assisted).