refactor: drop the inert per-agent budget_usd_per_month cap

[juliarvalenti]

Summary

Removes budget_usd_per_month, the per-agent monthly-spend cap that used to be enforced by the now-deleted daemon (gate_budget() in daemon/dispatch.py, checked before each claude -p cold-spawn). With cold-spawn gone, agents are resident sessions mycelium never meters, so the field had become a cosmetic manifest cap nothing reads — reporting a cap, not spend, and inviting false confidence ("this agent is capped at $5/mo" — it isn't).

Changes

CLI

• protocol.py: drop AgentManifest.budget_usd_per_month
• commands/agent.py: drop the --budget flag, budget= plumbing through build_manifest, the Budget column in agent ls, the budget line in agent show, and the summed-budget return from load_owned_agents
• commands/user.py: drop the summed-budget display in user show / whoami (text + JSON)
• commands/engine.py, integrations/{base,claude_code,cursor,engine}/dispatch.py: drop the budget param on build_manifest
• docs/principals.md: drop the "Cost roll-up" section

Backend

• schemas.py, routes/agents.py, routes/users.py, services/principals.py: drop budget_usd_per_month field + the summed-budget roll-up on users/teams

Frontend

• lib/api.ts: drop budget_usd_per_month from AgentSummary, OwnedAgent, User, Team

Docs

• Regenerated docs/concepts.html + docs/llms-full.txt from the updated principals.md source (docs/generate_docs.py)

Why stacked on refactor/remove-daemon-cold-spawn (#526)

Issue #525 explicitly depends on the daemon-removal PR landing first ("best done right after it lands so we're not editing the same manifest surface twice") — that PR deletes gate_budget() and the accumulation in daemon/dispatch.py/daemon/state.py. Since #526 was still open when this was picked up, this branch is based on refactor/remove-daemon-cold-spawn rather than main so the two don't collide. Retarget to main once #526 merges.

Testing

• Unit tests pass (uv run pytest tests/ -x -q) — CLI: 272 passed; backend: 407 passed, 6 skipped
• Linting passes (uv run ruff check .) — both CLI and backend
• Format check passes (uv run ruff format --check .) — both CLI and backend
• uv run ty check . clean (CLI + backend; only a pre-existing unrelated negmas import note in the sandbox)
• Frontend tsc --noEmit clean
• CLI↔backend SLIM+L9 wire-contract test unaffected (test_slim_l9_wire.py, both sides)

Related Issues

Closes #525

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Generated by Claude Code

[juliarvalenti]

Rebased onto main now that #526 has landed (used --onto to drop the daemon-removal commits this branch carried, which are already on main squashed) and retargeted the base main→. One reconciliation: routes/engines.py (native engine invite, merged in #523 after this branch was cut) still wrote budget_usd_per_month and passed it to AgentRead — dropped both so the route keeps working with the field gone. Gates green: backend ruff/ty + principals/engines tests, CLI ruff/format/ty + 296 tests, frontend tsc.