refactor: source EXTENSION_ID/ENV_VARS/OUTPUT_CHANNEL_NAME from constants

[MelbourneDeveloper]

TLDR

Wire the already-defined EXTENSION_ID, ENV_VARS, and OUTPUT_CHANNEL_NAME constants through their call sites so the brand name lives in exactly one place — src/constants.ts — instead of being re-hardcoded in six files.

Details

src/constants.ts already derived EXTENSION_ID, ENV_VARS, and OUTPUT_CHANNEL_NAME from the single BRAND_ID/BRAND_NAME/PUBLISHER roots, but the call sites still hardcoded the resulting strings. This replaces those literals with imports:

• src/logger.ts — drops the local const ENV_LOG_LEVEL_VAR = "DIFFR_LOG_LEVEL"; reads process.env[ENV_VARS.logLevel] instead.
• src/test/runTests.ts — DIFFR_E2E env key → [ENV_VARS.e2e]; launch-arg "nimblesite.diffr" → EXTENSION_ID.
• src/commands/flow.ts — error toast Output → Diffr → Output → ${OUTPUT_CHANNEL_NAME}.
• src/test/suite/{activation,commands,contentProvider}.test.ts — delete the three duplicated const EXTENSION_ID = "nimblesite.diffr" literals; import EXTENSION_ID from ../../constants.

No new files, no new dependencies, no behavioural change — the derived strings are byte-identical to the literals they replace. Net +10 / −15 across 6 files.

How Do The Automated Tests Prove It Works?

make ci passes end-to-end on this branch:

• E2E (@vscode/test-electron, real VSCode): activation.test.ts resolves the extension via the now-imported EXTENSION_ID and asserts every COMMAND_IDS value is registered; contentProvider.test.ts resolves diffr:// URIs against the seeded repo using the same imported id — proving the derived EXTENSION_ID matches the manifest's published id, otherwise getExtension(EXTENSION_ID) would return undefined and these suites would fail.
• runTests.ts launches the host with EXTENSION_ID and sets [ENV_VARS.e2e]; the suites only run because that wiring resolves correctly.
• Coverage gate held: Statements 95.09% (2153/2264), Functions 97.84%, Lines 95.09%, above the coverage-thresholds.json floor. tsc -p ., eslint src, and shipwright:validate all clean.

Breaking Changes

None. Internal refactor only; the env-var names, extension id, and channel label are unchanged.