feat(cli): cached shell completion (bash/zsh/fish)

[Sootopolis]

What

ccas completion <bash|zsh|fish> emits a self-contained, pure-shell completion script. The JVM boots once at install; at <TAB> the script runs entirely in the shell (no JVM, no network) → instant, all three shells. Completes subcommands, flags, club slugs (at slug positions) and recent job ids (ccas logs).

Why this shape (deviates from the issue's literal design)

#49 specified a hidden ccas __complete <argv> subcommand the shell calls per <TAB>. On a JavaAppPackaging binary that boots a JVM (~1.5s) every <TAB> — breaking the issue's own <50ms / cache-only acceptance. So instead:

• One CompletionSpec mirrors the CliCommand tree (single source of truth); CompletionEmitter generates all three shells from it.
• Committed completions/ccas.bash is the emitter's bash output (regenerate: ccas completion bash > completions/ccas.bash).
• Also retires the ~1.5s-per-<TAB> zio-cli dynamic script previously used for zsh/fish.

Dynamic sources

${XDG_CACHE_HOME:-~/.cache}/ccas/{clubs.txt,recent-jobs.txt}, written best-effort by normal commands (never alter exit code): staleness-gated GET /api/clubs refresh after a successful command; each submitted job id appended on submit.

Tests / guards (TestCcasCompletion)

• completions/ccas.bash == bash emitter output
• each emitted script passes <shell> -n (skips absent shells; @@ flaky to absorb fork-pressure flakes without masking real syntax errors)
• CompletionSpec ⊇ tree commands + flags, and value-vs-boolean flag classification matches the tree
• positional kinds pinned

Verification

• Full suite 791 green (4 new completion tests + completion parser case).
• Bash completion driven across 15 scenarios (subcommands, flags, variadic-vs-single slug positional gating, value-flag guard, nested blacklist/schedule, empty-cache no-op).
• Live end-to-end: real ccas-server (isolated schema) → ccas jobs refreshed clubs.txt → ccas stats … team-alpha submit wrote the real ULID to recent-jobs.txt (job Completed) → sourced completion served slugs + the ULID with prefix filtering.

Scoped out / notes

• Empty-cache default_clubs fallback → CLI config file resolution #43 (no CLI config yet).
• Hidden __complete JVM subcommand intentionally not built.
• fish offers slugs at every positional of single-slug commands (no portable positional-count); cosmetic, documented in CompletionEmitter. bash/zsh gate correctly.
• Drive-by: Main's serve branch now logs the crash cause (foldCauseZIO) instead of the error-swallowing fold (body of the deprecated ZIO#exitCode).

Closes #49. Part of epic #40.

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