refactor(sdlc): 消除四個 SDLC skill 間重複邏輯，改為委派唯一權威來源

What（做了什麼）：
1. 移除 plan、analyze、implement 三個 skill 及 README.md 中各自重述的 wiki hash 演算法說明（原本各處都各自寫一遍「取 SHA-1 前 8 碼大寫十六進位，開頭若為數字或 A/B/C 則替換為 H 加後 7 碼」），改為統一指向唯一權威工具 jsc-gitea/tools/hash-id（透過 jsc-gitea:wiki 使用）。
2. 移除 plan、analyze、implement、maintain 四個 skill 中重複的 model chain fallback 選擇邏輯說明（原本各自描述「執行 jsc-cli/tools/model-config.sh get {stage}，若印出 chain 則取目前 CLI 可用的第一個，fallback 依 chain 順序套用」），改為統一呼叫新的共用子指令 jsc-cli/tools/model-config.sh resolve {stage}，由該子指令自行封裝解析邏輯（此 resolve 子指令由另一位 agent 同時在 sibling repo jsc-cli 開的配套 PR 新增，本 PR 依賴該 PR）。
3. implement/SKILL.md 移除自身多餘的「先解析環境變數」步驟（原第 2 步，手動檢查 JSC_WIKI_REPO_ANALYZE、JSC_WIKI_REPO、JSC_WIKI_REPO_QUESTION、GITEA_HOST、GITEA_TOKEN 後才詢問使用者），因為此解析已由 implement 其他步驟委派的 jsc-gitea:wiki 正確處理，屬於死重複邏輯；後續步驟由 2-8 重新編號為 2-7。
4. maintain/SKILL.md 在 frontmatter description 欄位加入明確的負向觸發說明，釐清此 skill 僅用於已交付、仍在維護窗口內的專案，「不適用於仍在實作中或尚未登錄於 MAINTAIN_CONTENTS 的專案」。
5. plugin.json、.claude-plugin/plugin.json、.codex-plugin/plugin.json 三份版本號檔案，由 0.0.3 升版至 0.0.4。

Why（為什麼改）：
四個 SDLC skill 各自重述相同的 hash 演算法與 model chain fallback 邏輯，違反 jsc-meta:skill-check 稽核準則中「單一權威來源」的要求，日後維護容易改一處漏一處；implement 的環境變數解析步驟與其他步驟委派的 jsc-gitea:wiki 功能重疊，屬死碼；maintain 的觸發時機描述不夠明確，容易被誤用在尚未進入維護窗口的專案上。

How（怎麼改的）：
將重複邏輯抽離，改為指向或呼叫唯一權威工具/skill（jsc-gitea/tools/hash-id、jsc-cli/tools/model-config.sh resolve、jsc-gitea:wiki），移除 implement 中的死步驟並重新編號，於 maintain frontmatter 補上負向觸發描述，並同步升版三份 plugin.json。全程不改變任何對外行為，純屬重構。

Who（誰／哪個需求）：
jsc-meta:skill-check 對 plan、analyze、implement、maintain 四個 SDLC skill 的例行合規稽核修正。

skills/maintain/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: maintain
-description: SDLC maintenance stage. Gate on the designated model (model-config) or capability tags for the maintenance stage, lock the model via sdlc-gate, read projects still inside their maintenance window from MAINTAIN_CONTENTS, then run one sub agent per project: switch to develop or master, propose at least five maintenance actions, commit to a new branch, push, and PR. Update the last-maintained timestamp afterward. Use for periodic upkeep of delivered projects.
+description: SDLC maintenance stage. Gate on the designated model (model-config) or capability tags for the maintenance stage, lock the model via sdlc-gate, read projects still inside their maintenance window from MAINTAIN_CONTENTS, then run one sub agent per project: switch to develop or master, propose at least five maintenance actions, commit to a new branch, push, and PR. Update the last-maintained timestamp afterward. Use for periodic upkeep of delivered projects inside their maintenance window; not for projects still mid-implementation or not yet registered in MAINTAIN_CONTENTS.
 ---
 
 # maintain
@@ -11,7 +11,7 @@ All wiki reads and writes go through `jsc-gitea:wiki`.
 ## Steps
 
 1. **Model gate and stage lock**:
-   1. Resolve the maintain stage's designated model chain: run `jsc-cli/tools/model-config.sh get maintain`. If it prints a chain, the required model is the first entry of the chain the current CLI can use (fallbacks apply in chain order). If it prints nothing, fall back to the 「SDLC 階段需求」 table from `jsc-cli:models` (any listed model qualifies for maintenance).
+   1. Run `jsc-cli/tools/model-config.sh resolve maintain` to get the required model; if it prints nothing, fall back to the 「SDLC 階段需求」 table from `jsc-cli:models` (any listed model qualifies for maintenance).
    2. If the current model is not the required model, or is missing from the mapping table, block the flow and tell the user which model to switch to. Completion condition: the current model satisfies the gate.
    3. Lock the stage: run `jsc-hooks/hooks/sdlc-gate.sh lock maintain {current-model}`. From now until the next SDLC stage's gate runs, the sdlc-gate hook enforces this model on every prompt; switching models mid-stage gets blocked. Completion condition: the lock file is written, verified with `sdlc-gate.sh report`.
    4. Run this gate only when the stage changes; inside the maintenance stage the lock already enforces the model, so never re-gate between projects.