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>

base-action/bun.lock

@@ -1,14 +1,17 @@
 {
   "lockfileVersion": 1,
+  "configVersion": 0,
   "workspaces": {
     "": {
       "name": "@anthropic-ai/claude-code-base-action",
       "dependencies": {
         "@actions/core": "^1.10.1",
+        "shell-quote": "^1.8.1",
       },
       "devDependencies": {
         "@types/bun": "^1.2.12",
         "@types/node": "^20.0.0",
+        "@types/shell-quote": "^1.7.5",
         "prettier": "3.5.3",
         "typescript": "^5.8.3",
       },
@@ -31,12 +34,16 @@
 
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+    "@types/shell-quote": ["@types/shell-quote@1.7.5", "", {}, "sha512-+UE8GAGRPbJVQDdxi16dgadcBfQ+KG2vgZhV1+3A1XmHbmwcdwhCUwIdy+d3pAGrbvgRoVSjeI9vOWyq376Yzw=="],
+
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     "csstype": ["csstype@3.1.3", "", {}, "sha512-M1uQkMl8rQK/szD0LNhtqxIPLpimGm8sOBwU7lLnCpSbTyY3yeU1Vc7l4KT5zT4s/yOxHH5O7tIuuLOCnLADRw=="],
 
     "prettier": ["prettier@3.5.3", "", { "bin": { "prettier": "bin/prettier.cjs" } }, "sha512-QQtaxnoDJeAkDvDKWCLiwIXkTgRhwYDEQCghU9Z6q03iyek/rxRh/2lC3HB7P8sWT2xC/y5JDctPLBIGzHKbhw=="],
 
+    "shell-quote": ["shell-quote@1.8.4", "", {}, "sha512-VsC6n6vz1ihYYyZZwX7YZSF5l5x36ca17OC+a69h94YqB7X6XLwf+5MOgynYir2SLFUbl8gIYvBo8K8RoNQ6bQ=="],
+
     "tunnel": ["tunnel@0.0.6", "", {}, "sha512-1h/Lnq9yajKY2PEbBadPXj3VxsDDu844OnaAo52UVmIzIvwwtBPIuNvkjuzBlTWpfJyUbG3ez0KSBibQkj4ojg=="],
 
     "typescript": ["typescript@5.8.3", "", { "bin": { "tsc": "bin/tsc", "tsserver": "bin/tsserver" } }, "sha512-p1diW6TqL9L07nNxvRMM7hMMw4c5XOo/1ibL4aAIGmSAt9slTE1Xgw5KWuof2uTOvCg9BY7ZRi+GaF+7sfgPeQ=="],