feat(cli): multi-context simulation via --context flag

Add --context KEY=VALUE[,...] (repeatable) to glint check. When two or
more --context flags are given, glint evaluates every pipeline job across
all contexts and prints a side-by-side comparison table:

  glint check --context branch=main --context branch=develop .yml

Each column shows active / manual / skipped / blocked per job. Known
context keys are branch, tag, source (case-insensitive); any other
KEY=VALUE pair is treated as a CI variable override. The --changes /
--changes-from changed-file list is shared across all contexts. Implicit
branch=main / source=push defaults are skipped when --context is used.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ROADMAP.md

@@ -23,7 +23,7 @@ Pass `--branch`, `--tag`, `--source`, or `--var` to `glint check` or `glint grap
 - ~~**Workflow rule strict evaluation**~~ — ✓ shipped v0.2.14; unparseable `if:` skips the rule instead of matching everything; prevents wrong variables being injected
 - ~~**Single `=` operator**~~ — ✓ shipped v0.2.14; bare `=` accepted as alias for `==` in `rules:if:` expressions
 - ~~**`rules:changes:` evaluation**~~ — ✓ shipped v0.2.21; `--changes PATH` and `--changes-from REF` flags; doublestar glob matching (`*` within segment, `**` across segments); permissive when no file list provided
-- **Multi-context simulation** — run multiple contexts in one invocation and print a comparison table (`--context branch=main --context branch=develop --context tag=v1.0.0`)
+- ~~**Multi-context simulation**~~ — ✓ shipped v0.2.22; `--context KEY=VALUE[,...]`; repeatable; prints a comparison table of `active`/`manual`/`skipped`/`blocked` per job across all contexts
 - **Context-scoped linting** — skip `needs:`/`dependencies:` cross-checks for jobs that are statically unreachable in the given context
 
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