feat(loop-context): resolve token budget from loop-cost's pattern estimate

[KhaiTrang1995]

Summary

loop-context's circuit breaker only accepts --token-budget as a hand-typed
number, and loop-budget.md's "On budget exceed" section admits the budget
number itself is usually a guess. loop-cost already computes a realistic
per-run token estimate for every pattern and readiness level from
patterns/registry.yaml -- nothing connected the two.

What

Add --budget-from-pattern <id> to loop-context's CLI, plus --budget-level,
--budget-scenario, --budget-cadence, and --budget-conservative to shape
the lookup. It shells out to loop-cost's built CLI -- the same
monorepo-sibling-then-installed-dependency resolution loop-init already uses
for loop-audit -- so the two packages stay independent at the source level:

• An explicit --token-budget always overrides the derived value.
• An unknown pattern id surfaces loop-cost's own error message, not a silent
  fallback.

Also updates the loop-guard skill template and loop-cost's README, both of
which previously worked around the missing wiring with a manual JSON-parsing
shell pipe (BUDGET=$(... | node -e '...')) -- that hack is no longer needed
now that the flag does it directly.

Why this shape

• Mirrors the existing cross-tool integration pattern in this monorepo
  (subprocess to a built CLI, not a shared library import) rather than
  introducing a new dependency style.
• loop-cost has no dependency on loop-context, so no circular dependency.

Tested

tools/loop-context: 31/31 passing after a fully clean rebuild (wiped
node_modules/dist in both loop-context and loop-cost, reinstalled,
rebuilt). 13 new tests: resolver unit tests (scenario selection, unknown
pattern, invalid scenario rejected before spawning) and CLI integration tests
(budget resolved from pattern, explicit --token-budget overriding, unknown
pattern surfacing loop-cost's error). All pre-existing tests pass unmodified.
Version 1.0.0 -> 1.1.0

[cobusgreyling]

Thanks @KhaiTrang1995 — CI is green. This PR depends on the loop-cost orchestration changes in #256; we'll review/merge #256 first, then rebase this branch onto main. No action needed from you until #256 lands.

[cobusgreyling]

Merged on top of #256 — thanks @KhaiTrang1995! --budget-from-pattern wiring looks solid; 31/31 tests green after rebase. Published as loop-context v1.1.0.