feat(cli): .glint.yml config and inline suppression comments

Adds project-level configuration and per-job suppression directives:

.glint.yml (searched from pipeline dir up to the git root):
- ignore: [GL007, GL032] — suppress rules globally for the project
- severity: {GL004: warning} — override rule severity (error/warning/ignore)
- stages: [quality] — extra stages beyond the pipeline's stages: block
- token: / url: / cache_dir: — defaults for flags; lower priority than
  CLI flags and environment variables

Inline suppression (# glint: ignore):
- Place "# glint: ignore GL007" immediately before a job definition to
  suppress that rule for the specific job only
- Multiple rules: "# glint: ignore GL007, GL032" (comma or space separated)
- Wildcard: "# glint: ignore all" suppresses every finding for the job
- Suppressions are scoped to the annotated job; pipeline-level findings
  are unaffected
- Parsed from yaml.Node head/line comments in the first parse pass;
  stored in Pipeline.Suppressions (root file only, not includes)

New packages: internal/config (Load, walk-up search, .git boundary stop)
New files: cmd/glint/filter.go (applyConfig, isSuppressed helpers)
Tests: config_test.go, parser_suppress_test.go, filter_test.go
Validate fixtures: testdata/config_ignored/, config_severity/, config_suppress/

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

testdata/config_ignored/.gitlab-ci.yml

@@ -0,0 +1,10 @@
+stages:
+  - build
+
+# GL007 (only/except deprecated) would normally fire here, but the .glint.yml
+# in this directory ignores GL007.
+deprecated-job:
+  stage: build
+  only:
+    - main
+  script: echo ok

testdata/config_ignored/.glint.yml

@@ -0,0 +1,2 @@
+ignore:
+  - GL007

testdata/config_severity/.gitlab-ci.yml

@@ -0,0 +1,8 @@
+stages:
+  - build
+
+# GL004 (undefined stage) is demoted to warning by .glint.yml, so the exit
+# code must be 0 even though there is a finding.
+bad-stage-job:
+  stage: nonexistent
+  script: echo hi

testdata/config_severity/.glint.yml

@@ -0,0 +1,2 @@
+severity:
+  GL004: warning

testdata/config_suppress/.gitlab-ci.yml

@@ -0,0 +1,15 @@
+stages:
+  - build
+
+# glint: ignore GL007
+suppressed-job:
+  stage: build
+  only:
+    - main
+  script: echo ok
+
+still-flagged-job:
+  stage: build
+  only:
+    - main
+  script: echo ok