fix(hooks): JSON-escape GT_BIN path on Windows in resolveAndSubstitute (gt-1at)

[baumgold]

Fixes #3250

On Windows, GT_BIN paths contain backslashes (e.g. C:\\tools\\gt.exe). When substituted literally into a JSON template, raw backslashes produce invalid JSON.

Changes:

• Escape backslashes in resolveAndSubstitute before {{GT_BIN}} substitution
• Fix test reformatting to use json.MarshalIndent instead of strings.ReplaceAll(":", " : ") which was corrupting Windows drive letters (C: → C :)

[codecov-commenter]

❌ 5 Tests Failed:

Tests completed	Failed	Passed	Skipped
9319	5	9314	48

View the top 3 failed test(s) by shortest run time

github.com/steveyegge/gastown/internal/cmd::TestBuildRefineryPatrolVars_FullConfig

Stack Traces | 0s run time

=== RUN   TestBuildRefineryPatrolVars_FullConfig
    patrol_helpers_test.go:166: expected 5 vars, got 7: [target_branch=main integration_branch_refinery_enabled=true integration_branch_auto_land=false run_tests=true delete_merged_branches=true judgment_enabled=false review_depth=standard]
--- FAIL: TestBuildRefineryPatrolVars_FullConfig (0.00s)

github.com/steveyegge/gastown/internal/cmd::TestRunHooksSyncNonClaudeAgent

Stack Traces | 0.01s run time

=== RUN   TestRunHooksSyncNonClaudeAgent
Syncing hooks...
  ✓ mayor/.claude/settings.json (created)
  ✓ deacon/.claude/settings.json (created)
  ✓ myrig/crew/.claude/settings.json (created)
warning: role_agents[crew]=opencode - agent "opencode" binary "opencode" not found in PATH, falling back to default

Synced 3 targets (3 created, 0 updated, 0 unchanged)
    hooks_sync_test.go:366: opencode plugin not created in worktree alice
--- FAIL: TestRunHooksSyncNonClaudeAgent (0.01s)

github.com/steveyegge/gastown/internal/doctor::TestHooksSyncCheck_Fix_TemplateAgent

Stack Traces | 0.01s run time

=== RUN   TestHooksSyncCheck_Fix_TemplateAgent
warning: role_agents[crew]=opencode - agent "opencode" binary "opencode" not found in PATH, falling back to default
    hooks_sync_check_test.go:219: expected StatusWarning before fix, got OK
--- FAIL: TestHooksSyncCheck_Fix_TemplateAgent (0.01s)

github.com/steveyegge/gastown/internal/doctor::TestHooksSyncCheck_TemplateAgent_Missing

Stack Traces | 0.01s run time

=== RUN   TestHooksSyncCheck_TemplateAgent_Missing
warning: role_agents[crew]=opencode - agent "opencode" binary "opencode" not found in PATH, falling back to default
    hooks_sync_check_test.go:193: expected StatusWarning for missing template agent file, got OK: All 3 hook targets in sync
--- FAIL: TestHooksSyncCheck_TemplateAgent_Missing (0.01s)

github.com/steveyegge/gastown/internal/doctor::TestHooksSyncCheck_TemplateAgent_OutOfSync

Stack Traces | 0.01s run time

=== RUN   TestHooksSyncCheck_TemplateAgent_OutOfSync
warning: role_agents[crew]=opencode - agent "opencode" binary "opencode" not found in PATH, falling back to default
    hooks_sync_check_test.go:172: expected StatusWarning for out-of-sync template agent, got OK: All 3 hook targets in sync
--- FAIL: TestHooksSyncCheck_TemplateAgent_OutOfSync (0.01s)

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[baumgold]

Build Status Note

The CI failures on this PR are pre-existing failures on main, not introduced by this PR's changes:

• Lint: hooksDir is unused — fixed in fix(hooks-sync): use configured agent name for non-Claude hooks (gt-lch) #3242
• TestBuildRefineryPatrolVars_FullConfig — fixed in fix(hooks-sync): use configured agent name for non-Claude hooks (gt-lch) #3242

Merge order: #3242 must land first. Once merged, this PR's CI should pass.

The Windows-specific fix ({{GT_BIN}} backslash escaping + MarshalIndent test) is the only change here and all hooks tests pass locally.