Fix unreachableTrigger false positives for cross-spec and conditional trigger emissions (#19)

[yavorpanayotov]

Fixes #19.

Three fixes to the unreachable-trigger analysis, applied to both the Rust analyzer (crates/allium-parser/src/analysis.rs) and the TypeScript extension analyzer (extensions/allium/src/language-tools/analyzer.ts).

1. Qualified trigger calls are a valid trigger form

when: alias/Trigger(...) is documented in the language reference ("Responding to external triggers"), and the TS isValidTriggerShape already accepted it — but the Rust is_valid_trigger rejected it with an allium.rule.invalidTrigger error, making allium check exit non-zero on the issue's minimal repro (this was actually worse than the info-level diagnostics the issue reports). Expr::Call with a QualifiedName function is now a valid trigger.

2. Cross-spec trigger reachability across use imports

The CLI's CrossModuleContext now carries imported_triggers: per file, a use-alias → set of trigger names the aliased module provides (surfaces) or emits (rule ensures), computed by the new allium_parser::collect_trigger_outputs. The unreachable-trigger check (both the diagnostics lane and the analyse findings lane) resolves:

• alias/Trigger against the aliased module — flagged only when the module is in the check set and determinately lacks the trigger, with a message naming the module: ... but imported module 'emitter' does not provide or emit it.
• aliases whose targets are outside the check set (e.g. github.com/... coordinates) — never flagged, reachability is unknowable
• unqualified triggers — local provides/emits first, then any imported module's triggers

The single-file TS analyzer cannot see other modules, so it now skips qualified subscriptions entirely (call name preceded by /).

3. Emissions inside if/else if/else branches and for iterations

A trigger emitted as the leading call of a conditional branch or for body inside an ensures: value now registers as an emission. (Contrary to the issue's grammar-gap theory, the Rust parser already parsed these fine — the collector just didn't recurse.) Rust: collect_leading_ensures_call recurses into Conditional/For; TS: a branch-call lane scoped to ensures clause extents via the new ensuresClauseRegions helper, so branch calls in other clauses (e.g. a let conditional) don't register. for is included on both sides so the two implementations can't diverge on nesting.

Verification

• Issue's minimal repro: allium check emitter.allium listener.allium exits 0 with no invalidTrigger/unreachableTrigger for emitter/Pinged; analyse likewise
• Issue 2 repro: the else-branch SensorAdvertDecoded emission satisfies its listener
• Genuinely unreachable qualified triggers are still flagged (new message names the module)
• 357 Rust parser tests (10 new), 29 CLI integration tests (5 new), 320 extension tests (4 new) — all green; npm run lint clean

Specs updated in docs/project/specs/ and the parity notes in docs/project/rust-checker-parity.md.

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