docs: sync to Claude Code v2.1.278 (#183)

* docs: sync to Claude Code v2.1.278

Type: docs

Audit of the tutorial against Claude Code 2.1.278 (repo baseline was
2.1.263). Fixes claims the repo asserts that are now false; new-feature
coverage is English-only.

P0 - the repo stated the opposite of current behavior:
- AGENTS.md: the claude-md skill said Claude Code "does not read
  AGENTS.md directly" in all 5 languages. It has since v2.1.277, when no
  CLAUDE.md exists at or above the working directory.
- /output-style: listed as "Removed in v2.1.91" in 5 languages and in
  09-advanced-features. Re-added in v2.1.269; row moved out of the
  Deprecated Commands table.
- Permission rules: setup-auto-mode-permissions.py seeded Write(*),
  Glob(*) and NotebookEdit(*), which Claude Code accepts but never
  consults and warns about at startup. Removed; same fix in the
  config-examples.json profile and the 06/09 category tables.
- taskOutputMaxChars: documented as live. The TaskOutput tool was
  removed in v2.1.278 and the key is inert.

P1:
- Dynamic workflow "medium" guideline is fewer than 10 agents, not 15;
  the default is small on Pro plans since v2.1.271.
- Todo-tool availability restated as the official allowlist (Claude 3.x,
  Opus 4-4.7, Sonnet 4-4.6, Haiku 4.5) instead of a denylist; 23 sites
  across 5 languages.
- Memory hierarchy now notes the AGENTS.md fallback.
- Auto-mode classifier cost qualified: not charged on Enterprise plans
  and Claude API accounts since v2.1.278.

P3 (English only): full AGENTS.md section in 02-memory; omitClaudeMd
subagent field; plugin eval / --json / --accept-command / --marketplace;
maxEffortLevel, bashEditDiffEnabled, syncClaudeAi*, 4 env vars,
--system-prompt-snapshot, --plugin-dir folders; send-now key and Monitor
deadlines; checkpoints subagent-edit limitation.

Learning skills audited clean: 100 quiz questions and 100 Review
pointers all valid, 20 self-assessment options correctly mapped.

Cross-file anchors: 15 broken before, 15 after, 0 introduced.

* docs: address review — stale version stamps, /output-style re-add, permission tables

07-plugins/README.md

@@ -844,6 +844,40 @@ projected ctx: +1,420 tokens per turn  ·  +9,800 tokens per /review invocation
 
 LSP servers were added to the details pane in v2.1.142. See also the marketplace browse pane's projected context cost (v2.1.143) covered in [Plugin Marketplace](#plugin-marketplace).
 
+### `claude plugin eval` (v2.1.269+)
+
+`claude plugin eval` runs a plugin's eval suite and reports scored, reproducible results, so you can tell whether a change to a skill or agent actually improved it. Results come back as JSON plus an HTML report.
+
+```bash
+claude plugin eval            # Run the plugin's eval suite
+claude plugin eval --help     # Full option list
+```
+
+### Machine-readable output with `--json` (v2.1.268+)
+
+`--json` is accepted on `install`, `uninstall`, `update`, `enable`, and `disable`, which makes plugin management scriptable in CI. Each row of `claude plugin list --json` also carries `errorDetails` and `noteDetails`, so a failing plugin explains itself without a second command.
+
+```bash
+claude plugin install my-plugin@my-marketplace --json
+claude plugin list --json
+```
+
+### Accepting an exact command with `--accept-command` (v2.1.271+)
+
+`--accept-command <sha256>` on `install` and `update` accepts exactly the command a previous `--json` run displayed, in place of a blanket `-y`.
+
+```bash
+claude plugin install my-plugin@my-marketplace --accept-command <sha256>
+```
+
+### Installing from a marketplace you haven't added (v2.1.275+)
+
+In a session, `/plugin install <plugin> --marketplace <source>` names the marketplace inline and offers to add it before installing, so discovering and adding a marketplace is no longer a separate step. This is the in-session slash-command form, not a `claude plugin` CLI flag.
+
+```bash
+/plugin install code-reviewer --marketplace anthropics/claude-code-plugins
+```
+
 ## Installation Methods
 
 ### From Marketplace
@@ -1269,8 +1303,8 @@ The following Claude Code features work together with plugins:
 
 ---
 
-**Last Updated**: September 6, 2026
-**Claude Code Version**: 2.1.263
+**Last Updated**: September 19, 2026
+**Claude Code Version**: 2.1.278
 **Sources**:
 - https://code.claude.com/docs/en/plugins
 - https://code.claude.com/docs/en/plugins-reference