feat(cli): inject system prompt, AGENTS.md, and environment into TUI

[Astro-Han]

Summary

• Sink the read-only system-prompt fragment builders (workspace-instructions / AGENTS.md, personalization, project-context, session-environment) from apps/desktop/src/main into packages/runtime/src/system-prompt, shared by the desktop app and the CLI/TUI.
• Inject a systemPrompt (personalization + gated workspace instructions) and a per-turn turnTailPrompt (cwd/git/platform/date) into the CLI/TUI's AiSdkBackend. Previously the TUI agent ran with no system message at all.

Why

The CLI created its AiSdkBackend without a systemPrompt, so the agent had no AGENTS.md project instructions, no personalization, and no session environment — it ran "naked". Desktop already built these fragments in apps/desktop/src/main, but packages/cli cannot import from apps/desktop, so the logic had to be shared at the runtime layer.

Scope

4 commits, each independently revertible (dependency chain below):

1. refactor(runtime,desktop): sink workspace-instructions prompt builder — runtime file + index export + desktop workspace-instructions.ts (re-export read-only builder + keep open/create management surface)
2. refactor(runtime,desktop): sink personalization prompt builder — runtime file + index export + delete desktop personalization-prompt.ts + system-prompt-main/settings-ipc-helpers/tests import from @maka/runtime
3. refactor(runtime,desktop): sink project-context and session-environment builders — sunk together (session-environment imports ProjectGitInfo from project-context, must move together) + system-prompt-main/main/2 tests import changed
4. feat(cli): inject system prompt and per-turn environment into TUI backend — cli-system-prompt.ts + tests + runtime-bootstrap wiring

Dependencies and revert:

• feat (4) depends on all three refactor commits (imports the runtime fragments). Reverting any refactor must revert feat too.
• Reverting feat alone is safe (fragment sinking stays, desktop unaffected).
• Commits 1 and 2 are independent of each other; commit 3 binds project-context + session-environment together.

Not included (intentional, follow-up PRs):

• skills catalog + Skill tool for the CLI (needs buildSkillAgentTool wiring; another contributor is working on the skills module)
• LocalMemoryService for the CLI (stateful, desktop-only; sunk as an injected fragment in a later PR)
• shared aggregate buildSystemPrompt (after skills + memory are also sunk, desktop/CLI share one assembler)

Verification

• TDD: cli-system-prompt.test.ts written first (RED: stub threw not implemented), then implemented (GREEN: 6 tests pass). Covers the settings gate (enabled/disabled), AGENTS.md injection, personalization, the empty case, joining, and the turn-tail environment.
• Per-commit: commits 1/2 runtime build green; commit 3 runtime + desktop build:main green; commit 4 cli test 74 pass.
• Full suite: desktop test 1892 pass, runtime test 812 pass, cli test 74 pass, full typecheck green.
• Gap: commits 1/2 did not run desktop build:main (the working-tree main.ts is in final state and would falsely break, but the staged state is self-consistent); commit 3's desktop build:main green covers the final state. Per-commit empirical verification can be backfilled with git stash --keep-index if wanted.

User-facing impact

The TUI agent now receives the cwd's AGENTS.md/CLAUDE.md/GEMINI.md (gated by settings.workspaceInstructions.enabled), the user's personalization preferences, and a per-turn environment block (cwd/git/branch/platform/date). No desktop behavior change. Skills and local memory are not yet available in the TUI (follow-up PRs).

Reviewer notes

• The settings gate is preserved: the CLI reads the same workspace settings.json, so disabling workspaceInstructions in desktop also disables it in the TUI.
• session-environment stays in turnTailPrompt (per-turn), not in the durable system prompt, matching desktop, to avoid churning the system-prefix hash when date/branch change.
• @maka/runtime does not import @maka/storage: settings are read by the CLI caller and injected into buildCliSystemPrompt (per layering review).
• workspace-instructions sinking moves only the read-only builder; desktop keeps the open/create management surface (workspace-instructions.ts re-exports read-only + keeps management).