feat: dynamic environment filter from observed data

[ajianaz]

Problem

The Release Health page hardcoded only two environment options — production and development. SDKs sending other environments (e.g. staging from a Flutter app) had their data stored correctly, but there was no way to filter for it in the UI. Adding a new env required a code change every time.

Solution

Replace the hardcoded dropdown with a dynamic filter backed by a new endpoint that returns the distinct environment values actually observed for the project.

Changes

New endpoint: GET /api/0/projects/{slug}/environments → ["development", "production", "staging"]

Layer	File	Change
DB trait	trapfall-db/src/lib.rs	list_environments() method
SQLite impl	trapfall-db/src/sqlite.rs	SELECT DISTINCT environment UNION of release_health + transactions
Postgres impl	trapfall-db/src/postgres.rs	same query, $N placeholders
Store wrapper	trapfall-core/src/store.rs	expose list_environments
API	trapfalld/src/server.rs	route + handler
Spec	openapi.yaml	document endpoint
API client	web/src/lib/api.ts	listEnvironments()
UI	release-health/+page.svelte	dynamic envOptions derived from observed data

Design decisions

• UNION of release_health + transactions — both have a proper environment column on sqlite + postgres. events stores environment inside a JSON blob, so excluded. (Also, transactions aren't persisted yet per 1c: Add transactions + transaction_spans DB tables and queries #237, but the column exists and the query is forward-compatible.)
• Active filter always rendered — if filterEnv is restored from a URL param before the fetch resolves (or points to an env no longer in the DB), it still appears as a selected button rather than silently vanishing.
• NULL environments excluded; results sorted alphabetically.

Verification

• cargo fmt --all -- --check → clean
• cargo test -p trapfall_db --lib → 23 passed (incl. new test_list_environments_unions_release_health_and_transactions)
• cargo build -p trapfalld → ok
• npm run check → 0 errors (1 pre-existing warning in transactions page, unrelated)
• npm run build + npm run test → 5 passed

Result

Any environment an SDK reports — staging, qa, preview, anything — now appears in the filter automatically, no code changes needed.