feat: auto-install shell completions via install

[lockwobr]

Summary

• Auto-install bash, zsh, and fish shell completions in the install script, with OS-aware path resolution (Linux system dirs vs macOS Homebrew
  prefix detection) and user-local XDG fallback
• Add generate_completions_from_executable to the Homebrew formula in .goreleaser.yaml so brew install handles completions automatically
• Update installation docs to reflect automatic completions, document AICR_NO_COMPLETIONS=1 opt-out, and list completion file paths in the
  uninstall section

Test plan

• Run ./install on macOS — verify bash/zsh completions installed, fish skipped if not installed
• Run AICR_NO_COMPLETIONS=1 ./install — verify completions are skipped
• Run shellcheck ./install — no new warnings
• Run go test ./pkg/cli/ -run TestCompletion — existing completion tests pass
• Run goreleaser check — validates formula template with new line
• Verify uninstall docs list all paths the install script can write to

Motivation / Context

Closes #338

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)
• Build/CI/tooling

Component(s) Affected

• CLI (cmd/aicr, pkg/cli)
• API server (cmd/aicrd, pkg/api, pkg/server)
• Recipe engine / data (pkg/recipe)
• Bundlers (pkg/bundler, pkg/component/*)
• Collectors / snapshotter (pkg/collector, pkg/snapshotter)
• Validator (pkg/validator)
• Core libraries (pkg/errors, pkg/k8s)
• Docs/examples (docs/, examples/)
• Other: ____________

Risk Assessment

• Low — Isolated change, well-tested, easy to revert
• Medium — Touches multiple components or has broader impact
• High — Breaking change, affects critical paths, or complex rollout

Rollout notes:

Checklist

• Tests pass locally (make test with -race)
• Linter passes (make lint)
• I did not skip/disable tests to make CI green
• I added/updated tests for new functionality
• I updated docs if user-facing behavior changed
• Changes follow existing patterns in the codebase
• Commits are cryptographically signed (git commit -S) — GPG signing info

[github-actions]

Coverage Report ✅

Metric	Value
Coverage	74.4%
Threshold	70%
Status	Pass

Coverage Badge

![Coverage](https://img.shields.io/badge/coverage-74.4%25-green)

No Go source files changed in this PR.

[yuanchen8911]

Inline comments from cross-review (Claude Code + Codex + CodeRabbit)

[yuanchen8911]

Cross-Review Summary (Iterative Consensus)

Reviewers: Claude Code, Codex, CodeRabbit
Rounds: 2 (independent reviews → cross-review with AGREE/DISAGREE)
Consensus reached: Yes

Confirmed Issues (all three reviewers agree)

#	File	Line	Severity	Description
1	install (write_completion)	~119, 127	Major	mktemp creates files with 0600 permissions. After sudo mv to a system completion dir, non-root users can't read the file — completions silently fail. Add chmod 644 "$tmp_file" before the mv.
2	install (setup_fish_completions)	~170	Minor	Fish completions only install to user dir (~/.config/fish/). Under sudo, this goes to /root/.config/fish/. Unlike bash/zsh which try system dirs first, fish has no system-dir fallback.
3	install	~407	Minor	`setup_completions

Contested Issues (2-1 split)

#	File	Severity	Description	For	Against
4	install (~L139, ~L157)	Minor	Hardcoded [[ -d /opt/homebrew ]] duplicated in bash+zsh functions.	Claude Code, CodeRabbit	Codex — standard ecosystem idiom; brew --prefix requires brew in PATH which isn't guaranteed under sudo; no realistic false-positive.

Dismissed Findings

• Orphaned temp file on sudo mkdir path (CodeRabbit) — Dismissed by Claude Code + Codex: the -w "$target_dir" check correctly routes to sudo mv when the dir is root-owned, and both branches clean up temp files on failure.

Positive Observations

• Clean per-shell function separation with proper error handling
• AICR_NO_COMPLETIONS=1 opt-out is good UX
• XDG fallback for user-local installs is well implemented
• Non-empty output validation before installing completion files
• .goreleaser.yaml uses standard Homebrew DSL correctly

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Iterative cross-review by Claude Code + Codex + CodeRabbit (2 rounds)

[yuanchen8911]

Inline comments from iterative cross-review (Claude Code + Codex + CodeRabbit, 2 rounds)

[mchmarny]

/lgtm

overriding to unblock, blocker already resolved