feat(ws-changed): filter and classify a changeset by file extension

[pyramation]

Summary

ws-changed answers "which packages are affected?" but has no notion of what kind of file changed, so a CI lane can only ask the one coarse question. That's how a diff of three package.json script strings ends up rebuilding a dev image and running a SQL lint lane. git-changed already has ext/include/exclude; this teaches ws-changed the same filter, plus the reporting a lane needs to decide on its own.

A FileFilter narrows the changed files before they're attributed to packages, so the same diff answers several questions:

// which packages have changed SQL? (and their dependents)
wsChanged({ overrides: { provider: 'pgpm', files: { ext: '.sql' } } }).result.packages;

// what kind of change was it, per package?
wsChanged().result.extensionsByPackage; // { 'my-pkg': ['.md', '.ts'] }

Filtering before ownership is the point, and it has two consequences worth stating:

• a dropped file can't make a package changed, and it also can't trigger global — a .sql lane isn't told "everything is affected" by a changed pnpm-lock.yaml. Ask the unfiltered question when you want the lockfile's blast radius;
• extensionsByPackage covers changed packages only, never dependents — they own no changed file, so "what changed in pkg" stays distinct from "what pkg is affected by".

New on AffectedResult:

extensions: string[];                            // ['.sql', '.ts'] across the changeset
extensionsByPackage: Record<string, string[]>;   // { core: ['.sql'] }
ignored: string[];                                // changed paths the filter dropped

ext accepts the shapes git-changed accepts ('sql', '.sql', 'ts,tsx', ['.ts','.tsx']), normalized to lowercased .ext, so a filter moves between the two packages without translation. extOf deliberately treats a dotfile or extensionless name as having no extension (.gitignore, Makefile, bin/ws-changed → ''), which means they match no ext filter rather than accidentally matching every one.

Surfaces: files in config, WS_CHANGED_EXT in the environment (so a CI lane needn't carry its own config file), and --ext / --files / --not-files / --exts on the CLI:

ws-changed --provider pgpm --ext .sql --exts
ws-changed --ext ts,tsx --not-files '**/generated/**'

77 tests pass; new coverage includes uppercase/multi-dot/dotfile extensions, absolute paths, include/exclude globs, a filtered-out global trigger, and dependents staying out of extensionsByPackage.

Follow-up, not here: routing constructive-db's dev-image.yml and proxy-e2e-tests.yaml through this instead of blanket YAML paths: entries.

Link to Devin session: https://app.devin.ai/sessions/0512ac5790334f939a7bd0c2a8442162
Requested by: @pyramation

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