fix: #7 — feat(install): one-line install.sh

[MiaoDX]

Closes #7.

Adds the install.sh one-shot installer plus an end-to-end Go test
harness that exercises it against a fake release tarball — no network
required in CI.

What's in this PR

• install.sh — POSIX bash. Detects OS (darwin/linux) and arch
  (arm64/x86_64), downloads the matching scripture-mcp release
  tarball from https://github.com/MiaoDX/verse-driven/releases/download/<tag>/scripture-mcp-<tag>-<os>-<arch>.tar.gz,
  unpacks it, and installs to ~/.local/bin/scripture-mcp (overridable
  with --prefix). Re-running overwrites the binary in place — that's
  the upgrade path. After install, it detects claude and codex on
  $PATH and runs scripture-mcp init --target=<agent> for each (which
  is already idempotent on configs via PR fix: #4 — feat(core): stdio MCP server + CLI subcommands #14's marker-fenced splice).
• --uninstall reverses both halves: init --uninstall for each
  detected agent, then removes the binary.
• Convenience flags: --no-wire installs the binary only;
  --yes/-y auto-confirms; --version <tag> pins a release;
  --from-archive <path> bypasses the network and unpacks a local
  tarball — used by the test harness, also handy for air-gapped
  installs or behind a corporate proxy. Env overrides
  RELEASE_BASE_URL / LATEST_RELEASE_URL exist for advanced cases.
• Prompting under curl | bash: prompt_yes reads from /dev/tty
  when stdin is the curl pipe, so the y/n confirmation actually reaches
  the user. When neither stdin nor /dev/tty is a terminal (CI, fully
  automated runs), it defaults to yes — --yes makes that explicit.
• internal/installer/install_test.go — Go tests that build the
  real scripture-mcp binary, pack it into a .tar.gz, then drive
  install.sh against a sandboxed HOME and a stubbed PATH.
  Covered:
  • --help surface lists all the documented flags.
  • Unknown flag → exit 2.
  • End-to-end three-phase cycle: fresh install + wire (asserts binary
    is executable, both ~/.claude/settings.json and
    ~/.codex/config.toml gain the >>> verse-driven block) → re-run
    (asserts "already up to date" for both configs and binary still
    present, i.e. idempotent) → --uninstall (asserts binary removed
    and snippets stripped).
  • No-agents case: missing claude/codex still installs the binary
    and reports "no supported agents detected".
  • --no-wire skips agent wiring even when both are on $PATH.
  • Missing --from-archive file fails fast with a clear diagnostic.
• README — replaces the prior "Install (planned)" section with a
  real one centered on install.sh, drops the speculative brew
  line per the issue's note.

Acceptance-criteria mapping

• install.sh detects OS/arch, downloads the right binary release, places it on PATH (warns when $PREFIX isn't on $PATH)
• Detects which agents are installed (claude / codex on PATH) and offers to wire each
• Calls scripture-mcp init --target=... per detected agent
• Re-running upgrades the binary and is idempotent on configs (asserted by TestInstallEndToEnd phase 2)
• Uninstall path: scripture-mcp init --uninstall --target=... removes the snippets — both surfaced directly via init and bundled into install.sh --uninstall

Verification

• go test ./... — green across all 9 packages, including 6 new installer tests
• go vet ./... — clean
• bash install.sh --help — prints flag table
• bash install.sh --bogus — exits 2 with "unknown flag" diagnostic
• End-to-end smoke (replicated by TestInstallEndToEnd):
  1. Build scripture-mcp and pack into /tmp/scripture-mcp.tar.gz.
  2. HOME=/tmp/h PATH=/tmp/agents:... bash install.sh --from-archive /tmp/scripture-mcp.tar.gz --prefix /tmp/bin --yes
     → installs /tmp/bin/scripture-mcp, splices the verse-driven block into both ~/.claude/settings.json and ~/.codex/config.toml.
  3. Re-running prints "already up to date" for both configs.
  4. bash install.sh --prefix /tmp/bin --uninstall strips the snippets and removes the binary.

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