Add memory plugin: three-tier markdown store with plugin-driven retrieval

A durable memory layer for OpenCode. Structure:

  ROOT.md          total plan: goals, hard rules, directory registry,
                   and a scenario -> file routing table
  <category>/
    index.md       one line per file, COMPILED from frontmatter
    <slug>.md      the memory itself

Two roots, same shape: <config>/memory/ (global) and
<project canonical>/.memory/ (project). Project wins on conflict; global
hard rules stay resident everywhere.

Why a plugin rather than a skill that tells the model to read a folder:
model-driven retrieval is unreliable — the model forgets, reads half the
files, or reads the wrong ones. Markdown is the human-facing format; the
plugin is the engine that parses, scores, and injects.

Measured, not assumed: FTS5's two built-in tokenizers both fail on this
corpus. On SQLite 3.53.4 with "部署脚本用 pnpm 而不是 npm...": unicode61
emits 7 terms for the whole sentence and matches 0 hits for "部署";
trigram needs >= 3 characters and also returns 0 for that two-character
word. So tokenization happens in the plugin (CJK bigrams, latin words)
and no SQL index is used — a thousand memories are fine to scan.

index.md and ROOT's two tables are compiled, never hand-edited: a
hand-maintained index drifts, a generated one cannot. Hit counters live
in .state.json so cross-device sync does not conflict on every recall.

Tools are named recall/remember/forget/inspect rather than
write/read/status: generic names were observed shadowing the harness's
own built-in tools.

memory/pitfalls/index.md

@@ -0,0 +1,8 @@
+# pitfalls 索引
+
+<!-- auto:begin pitfalls
+
+| 文件 | 概述 | 重点 |
+|---|---|---|
+| sqlite-cjk-tokenizer.md | unicode61 把整段中文当一个 token，trigram 漏掉两字词，必须自己分词。 | 实测：unicode61 查"部署"=0 命中；trigram 查"部署"=0 命中（需≥3字符） |
+<!-- auto:end

memory/pitfalls/sqlite-cjk-tokenizer.md

@@ -0,0 +1,23 @@
+---
+id: pitfalls/sqlite-cjk-tokenizer.md
+kind: fact
+summary: unicode61 把整段中文当一个 token，trigram 漏掉两字词，必须自己分词。
+highlight: 实测：unicode61 查"部署"=0 命中；trigram 查"部署"=0 命中（需≥3字符）
+created: 1791512161994
+updated: 1791512161994
+load_when:
+  - SQLite
+  - FTS5
+  - 全文检索
+  - 分词
+  - 中文检索
+---
+
+在 SQLite 3.53.4 上实测，字符串「部署脚本用 pnpm 而不是 npm，因为 lockfile 不兼容」：
+
+- `unicode61`（FTS5 默认）把 `部署脚本用` 当作**一个 token**，整句只产生 7 个词条。查「部署」0 命中，查「部署脚本」也 0 命中。子串永远匹配不上。
+- `trigram` 要求查询 ≥3 字符。词表是「不兼」「而不」「m，因」这种三字滑窗。查「部署」0 命中，查「部署脚」1 命中。
+
+中文里「部署」「配置」「依赖」「接口」这类**两字词占比极高**，trigram 漏掉的正好是最常用的一批。
+
+解法：索引前自己切 CJK 字符二元组，拉丁走 porter 词干，FTS5 只当倒排索引用。