feat(cli): 3 UX fixes — compact --help, silent plugin update sub-output, --json minified (v3.2.15)

[kengio]

Summary

3 UX fixes from live testing of v3.2.14 / this turn — bundled into one PR per user request.

A. `--help` compact-with-wrap (revert v3.2.12 long-format)

v3.2.12's blanket `next_line_help = true` made every arg render in long format. User testing flagged "ดูยาก" (hard to read). v3.2.15 reverts to compact AND wraps `[default]/[possible values]` to indented next line:

```
Options:
--vault Override vault root (highest priority · beats ONEBRAIN_VAULT and walk-up)...
-o, --output Output format. Default `text` is TTY-friendly; pipe-detected calls drop color/pretty automatically
[default: text, possible values: text, json, yaml, table, tsv]
--json Shorthand for `--output json`
```

Same wrap applied to `harness run --help` and `skill run --help` for `--mode` / `--harness`. `HarnessMode` variant docs stripped (the multi-line Possible values block was forcing long format).

B. `plugin update` no header leak

User testing of v3.2.14 flagged that 5 `▸ ` lines from `vault_sync`'s TtyProgress leaked ABOVE the framed `⚡ Plugin Update` header. v3.2.15 routes through new `vault_sync::run_silent` which forces `progress_writer = Some(io::sink())` — kills the per-step TTY lines AND the intro/outro frame. The framed header now appears as the FIRST thing in the report (right after the brand banner), with the animated spinner as the only progress signal — matches `doctor`/`update`.

`run_embedded` removed (no remaining caller; the in-between mode wasn't useful).

C. `--json` minified by default

Pre-3.2.15 auto-prettified JSON on TTY, which was convenient for humans glancing at a structured response but made the "copy/paste into curl / a script" path noisier than necessary. v3.2.15: `--json` (and `--output json`) emit single-line minified JSON by default; `--json --pretty` opts into indented.

```bash
$ onebrain --json plugin update --dry-run
{"version":"1","command":"plugin.update","ok":true,"data":{...},"warnings":[]}

$ onebrain --json --pretty plugin update --dry-run
{
"version": "1",
...
}
```

Test impact

• 1284 passed; clippy clean; fmt clean.
• Renamed: `root_help_renders_long_format` → `root_help_renders_compact_with_wrapped_defaults` (now asserts the new shape positively).
• Updated: `json_shortcut_picks_json_mode` → split into `_minified_by_default` + `_with_pretty_flag_is_indented`. Same for `output_flag_json`.

Files

```
CHANGELOG.md | 8 +++-
Cargo.lock | 8 ++--
Cargo.toml | 2 +-
crates/onebrain-cli/src/cli.rs | 53 ++++++++++++++++----------
crates/onebrain-cli/src/commands/vault_sync.rs | 32 ++++++++++++----
crates/onebrain-cli/src/output/mode.rs | 41 ++++++++++++++++----
crates/onebrain-cli/src/v31/plugin_update.rs | 13 ++++---
crates/onebrain-cli/tests/v31_integration.rs | 51 +++++++++++++++++--------
8 files changed, 145 insertions(+), 63 deletions(-)
```

⚠️ Do not auto-merge

User testing locally before merge per their request. Ready to review when they're back.