feat: add claude_args passthrough and structured_output (closes #1)

Bring the upstream v1 `claude_args` input and `structured_output` output
into this Gitea fork so downstream workflows can run the agent with
arbitrary Claude CLI flags (notably `--json-schema`) and read the
schema-validated verdict back as an action output, without an
agent-written file.

Approach (issue Option B, ported rather than bumped): the production
"Run Claude Code" step previously delegated to the external
anthropics/claude-code-base-action@v0.0.63, which has neither input.
Upstream base-action main has them but has migrated to the Claude Agent
SDK — a wholesale divergence that would change v0.0.63 behavior every
downstream step relies on. Instead this invokes the vendored base-action
directly via `bun run ${github.action_path}/base-action/src/index.ts`
(the same github.action_path pattern prepare.ts already uses, reliable
on Gitea), and ports only the two features onto the v0.0.63 process-spawn
engine.

- base-action/src/run-claude.ts: tokenize claude_args with shell-quote
  (comment-line stripping; quoted/file-path schemas survive intact) and
  append after the byte-identical BASE_ARGS, so empty claude_args yields
  an unchanged arg list; extract structured_output from the stream-json
  result event when --json-schema is present, failing loudly if absent.
- base-action/src/index.ts: forward INPUT_CLAUDE_ARGS.
- base-action/action.yml: add claude_args input + structured_output output.
- action.yml: add claude_args input + structured_output output; replace
  the external base-action delegation with a direct bun-run of the
  vendored copy (full INPUT_*/provider env contract derived from the
  vendored validate-env/index); bump the default Claude CLI install to
  2.1.160 (--json-schema requires a newer CLI than 1.0.117).
- shell-quote added to both package.json files; root bun.lock reconciled
  (it was stale vs package.json — non-frozen installs already resolved
  the newer tree).
- Tests for tokenizer, hasJsonSchema, and structured-output extraction.
- README: inputs/outputs tables, "Structured output" + "Version pins".
- examples/gitea-structured-output.yml.

Follow-up (cannot be done from this repo): consumers using a pre-baked
runner image (path_to_claude_code_executable) must rebuild that image
with a --json-schema-capable Claude CLI and restart the runner.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

examples/gitea-structured-output.yml

@@ -0,0 +1,64 @@
+# Example: schema-validated PR review verdict via `claude_args` + `structured_output`.
+#
+# Instead of having the agent write its verdict to a file, this asks Claude for a
+# result that conforms to a JSON Schema and reads it back from the action output.
+# Requires a Claude CLI new enough to support `--json-schema` (see README →
+# "Structured output"). If you consume this action through a pre-baked runner
+# image (path_to_claude_code_executable), that image's CLI must be bumped too.
+
+name: Claude PR Review (structured output)
+
+on:
+  pull_request:
+    types: [opened, synchronize]
+
+jobs:
+  review:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
+      issues: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      # The schema the verdict must conform to. Using a file (rather than an
+      # inline string) keeps the value free of spaces and `$` characters, so a
+      # schema with $ref/$defs survives shell tokenization intact.
+      - name: Write review schema
+        shell: bash
+        run: |
+          mkdir -p .gitea
+          cat > .gitea/review-schema.json <<'JSON'
+          {
+            "type": "object",
+            "additionalProperties": false,
+            "required": ["decision", "summary"],
+            "properties": {
+              "decision": { "type": "string", "enum": ["approve", "request_changes", "comment"] },
+              "summary": { "type": "string" }
+            }
+          }
+          JSON
+
+      - name: Run Claude review
+        id: review
+        uses: ryan/claude-code-gitea-action@gitea
+        with:
+          gitea_token: ${{ secrets.GITEA_TOKEN }}
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          direct_prompt: |
+            Review the changes in this pull request and return your verdict
+            strictly matching the provided JSON schema.
+          claude_args: --json-schema ${{ github.workspace }}/.gitea/review-schema.json
+
+      - name: Act on the verdict
+        shell: bash
+        env:
+          VERDICT: ${{ steps.review.outputs.structured_output }}
+        run: |
+          echo "Decision: $(echo "$VERDICT" | jq -r '.decision')"
+          echo "Summary:  $(echo "$VERDICT" | jq -r '.summary')"