fix: mark unused context parameter in post-startup-notifications activate

[sachinh-amazon]

Issue

Description of Changes

Fixes a TypeScript compile break in the SageMaker build. The code-editor-sagemaker-server "Build artifacts" step fails with:

extensions/post-startup-notifications/src/extension.ts(11,26): error TS6133: 'context' is declared but its value is never read.
tsgo exited with code 2

The post-startup-notifications extension's activate(context: vscode.ExtensionContext) no longer references context in its body (its previous consumers were removed in #236), and the extension's tsconfig inherits noUnusedParameters: true, so the unused parameter is a hard compile error.

This change renames the parameter to the underscore-ignored form (_context) — the standard TypeScript convention for an intentionally-unused parameter — via the patches/sagemaker/post-startup-notifications.diff quilt patch. One-line change; no behavior change.

Testing

• Reproduced the exact CI error against the extension's own tsconfig.json with tsgo (the same compiler the build uses): the original context param → TS6133.
• With the fix (_context): tsgo --project ./tsconfig.json --noEmit → exit 0, no diagnostics.
• Patch regenerated via quilt (not hand-edited); diff is a single line and preserves the repo's code-editor-src/ path-prefix convention.

Screenshots/Videos

N/A

Additional Notes

Pre-existing latent break on main only: commit 5769285 (#236, 2026-06-10) removed the consumers of context but left the activate signature. main has #236; the 1.0/1.1/1.2 release branches do not, which is why only main fails to build. Unrelated to recent security-scan / dependency changes (those patches apply and compile cleanly). Surfaced now because this build ran against main.

Backporting

Not needed for 1.0/1.1/1.2 (they don't contain #236). If #236 is ever cherry-picked to a release branch, this one-line fix should accompany it.

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