fix: #4 — feat(core): stdio MCP server + CLI subcommands

[MiaoDX]

Closes #4.

Wires the full v0.1 binary surface. One executable now exposes
serve, lookup, lookup-from-prompt, recap, and init, with a
stdio MCP server that publishes four tools.

What's in this PR

• internal/mcp/server.go — minimal JSON-RPC 2.0 stdio MCP server
  (NDJSON framing). Implements initialize, tools/list, tools/call,
  ping, shutdown, and the notifications/initialized notification.
  Tool-level failures are returned as result-with-isError per MCP
  convention; transport-level failures become JSON-RPC error objects.
  Zero non-stdlib dependencies — the surface is small enough (3 methods,
  4 tools, no resources/prompts) that pulling in an MCP SDK would
  double the project's dependency footprint for very little gain.
• internal/cli/{cli,lookup,recap,init}.go — subcommand handlers. The
  flag parser tolerates flags placed after positional args
  (lookup "John 3:16" --format=json) per the issue spec. JSON is the
  default lookup output.
• lookup-from-prompt accepts both Claude (/bible John 3:16) and
  Codex ([[bible:John 3:16]]) marker styles. It reads either a raw
  prompt or a JSON object with a prompt/user_prompt field on stdin
  (the latter is the form Claude Code / Codex hooks send) and emits an
  additionalContext envelope on stdout suitable for both
  UserPromptExpansion and UserPromptSubmit. With no marker it
  exits 0 silently so hooks add nothing to the prompt. Trailing user
  prompt text after the reference is handled by progressively trimming
  tokens from the right until the resolver accepts what remains.
• recap — Mode B terminal print. --tradition= filters,
  --first-letter masks all-but-first character of each word/Han
  glyph for memory mode, --seed=N makes selection deterministic.
  Recap output goes to stdout only; the contract that it never enters
  a model_call input is enforced by where the agents invoke it
  (Claude Stop hook, Codex cdx shell wrapper) — both land in feat(claude): Claude Code adapter (Mode A + Mode B + skill) #5/feat(codex): Codex adapter (Mode A + Mode B) #6.
• init --target={claude-code,codex} [--recap=on|off] [--uninstall] [--dry-run] — splices a marker-fenced snippet into
  ~/.claude/settings.json or ~/.codex/config.toml. Idempotent
  (a second run reports "already up to date"); --uninstall strips
  the block and collapses the surrounding blank line; user content
  outside the markers is preserved. The Claude snippet matches
  plan.md §5.1; the Codex snippet matches §5.2.
• internal/injector/envelope.go — renders the §6.3 reflection
  envelope wrapping verse text in <scripture_card> tags with the
  "do not preach / quote verbatim" framing. DisplayRef formats the
  verse's reference for human display, switching by tradition.
• internal/packs/lookup.go — shared LookupReference(r resolver.Reference)
  and ReferenceID(r) helpers, used by both internal/cli and
  internal/mcp so the resolver→pack-id mapping has a single
  authoritative implementation. Returns packs.ErrNotBundled when the
  reference resolves to a tradition shipped api-only in this build
  (heart-sutra, quran), distinct from a hard "id miss" error.

Acceptance-criteria mapping

• scripture-mcp serve launches a stdio MCP server
• MCP tools: lookup, search, random, list_traditions —
  all return verses with checksum_sha256 and source
• Speaks the snippet from plan.md §5.1 (Claude Code) and §5.2
  (Codex) — init writes those snippets verbatim
• scripture-mcp lookup "<ref>" --format=json → JSON Verse on
  stdout (default; --format=text for terminal-pretty)
• scripture-mcp lookup-from-prompt reads stdin, emits
  additionalContext JSON suitable for both Claude
  UserPromptExpansion and Codex UserPromptSubmit
• scripture-mcp recap [--tradition=<t>] [--terminal] prints
  pretty terminal output, exit 0
• scripture-mcp recap --first-letter prints first-letter pattern
• scripture-mcp init --target={claude-code,codex} merges config
  snippet without overwriting; idempotent; supports --uninstall
  and --dry-run
• p50 latency for MCP lookup < 5 ms — verified by
  TestLookupLatency (200 trials over the in-memory registry)

Tests

• internal/mcp/server_test.go — initialize, notifications-have-no-
  reply, tools/list exposes all four, tools/call for each tool
  including the missing-verse → tool-error path, parse-error framing,
  unknown-method → method-not-found, and the p50 latency check.
• internal/cli/lookup_test.go — JSON default, JSON/text formats,
  ambiguous → exit 3, unrecognized → exit 1, sutra → "not bundled"
  message, plus marker-scan tests for slash and inline forms (with
  trailing prompt text), JSON input form, and silent-on-no-marker.
• internal/cli/recap_test.go — deterministic with seed, tradition
  filter, first-letter mask (ASCII + Han), unknown-tradition exit.
• internal/cli/init_test.go — file creation, recap-on/off variant,
  idempotent rerun, user-content preservation, uninstall, codex TOML
  output, missing-target → exit 2, dry-run.
• internal/injector/envelope_test.go — envelope wrapper structure
  and per-tradition DisplayRef cases.
• internal/packs/lookup_test.go — ReferenceID mapping incl.
  multi-word and numbered books, error cases, LookupReference
  happy/api-only/miss paths.

Verification

• make all (lint + verify-packs + test + build) clean
• Smoke test: ./bin/scripture-mcp lookup "John 3:16" --format=json
  resolves, returns canonical verse with checksum
  8473c0b1c7664945528317faf77351258eb79f8b11ba821ef76d7e916cde711a
• Smoke test: piping three JSON-RPC requests
  (initialize / tools/list / tools/call lookup John 3:16) into
  scripture-mcp serve returns protocolVersion 2024-11-05, the
  full tool list, and the verse with matching checksum

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