fix: replace --append-system-prompt-file with --append-system-prompt

[whitmo]

Summary

• P0 FIX: Claude CLI v2.1.63 does not support --append-system-prompt-file. All agent spawning was blocked.
• Changed all command construction sites to use --append-system-prompt with inline content instead.
• For tmux-based launches (runner.go, daemon.go, cli.go startClaudeInTmux): uses $(cat 'file') shell expansion so the prompt file is read at execution time.
• For exec.Command-based launch (cli.go restartClaude): reads the file in Go via os.ReadFile and passes content directly as an argument.
• Updated tests, doc.go, and README.md references.

Files Changed

File	Change
pkg/claude/runner.go	buildCommand() uses --append-system-prompt "$(cat '...')"
pkg/claude/runner_test.go	Updated test expectations
pkg/claude/doc.go	Updated flag reference
pkg/claude/README.md	Updated CLI flags table
internal/daemon/daemon.go	Fixed direct command construction
internal/cli/cli.go	Fixed both restartClaude (exec.Command) and startClaudeInTmux

Opportunities (not implemented)

• docs/AGENTS.md, docs/CRASH_RECOVERY.md, SPEC.md, ARCHITECTURE.md still reference the old flag name in documentation/examples — these are doc-only, non-blocking.

Test plan

• go test ./pkg/claude/... — all 20 tests pass
• go test ./internal/... — all internal tests pass
• go build ./... — full build succeeds
• No Go source files reference --append-system-prompt-file

🤖 Generated with Claude Code

[whitmo]

Triage Review

Priority: P0 (bug fix - blocks all agent spawning)
Build: Pass
Tests: Pass (all 20 claude tests + daemon + cli)
Merge conflicts: None - merges cleanly with main and all other open PRs
Roadmap alignment: Critical bug fix - --append-system-prompt-file flag doesn't exist in Claude CLI v2.1.63

Recommendation: Merge first - this is a blocking bug fix with no conflicts.

[whitmo]

Local CI Verification (2026-03-12)

Check	Result
go build	PASS
go vet	PASS
go test ./...	PASS (all packages)

CI Status: No GitHub Actions checks are running — this is expected for first-time fork PRs. GitHub requires a maintainer to approve workflow runs for PRs from forks.

Branch is rebased on upstream/main (0 commits behind). Ready for maintainer review and CI approval.