feat(quest): emit deprecation notice for quest_clear alias

[kunallanjewar]

Summary

• Adds a one-line migration gradient to quest_clear (MCP alias) and guild quest clear (cobra alias) so agents and users see a pointer to the canonical quest_fulfill verb.
• quest_fulfill output is unchanged — alias-only.
• JSON mode is unaffected — notice only appears in human-rendering paths.

The notice

⚠️ [deprecated] quest_clear will be removed — use quest_fulfill

Implementation

• internal/command/command.go: new CLIAliasDeprecations map[string]string field on Command[I,O] — maps alias name → notice string
• internal/command/cobra.go: cobraRunE checks cc.CalledAs() against the map after rendering; writes notice to cc.ErrOrStderr() (human mode only; the JSON path returns early before this code runs)
• internal/quest/clear_cmd.go: defines clearDeprecationNotice const; sets FulfillCommand.CLIAliasDeprecations["clear"]; overrides ClearCommand.MCPFormat to call formatFulfilled and append the notice

Acceptance criteria

• MCP quest_clear response includes ⚠️ [deprecated] quest_clear will be removed — use quest_fulfill
• CLI guild quest clear ... writes the notice to stderr (not stdout)
• --json mode is unaffected — notice never injected into JSON output
• quest_fulfill response does NOT contain the notice
• TestClearCommand_MCPBackwardCompat extended to assert deprecation line in MCP text output
• New TestCLI_QuestClearDeprecationStderr asserts stderr contains notice and stdout does not; sub-test asserts --json has no leakage
• make check passes

Sample --json output (no leakage)

{"result":{"Cleared":{"id":"QUEST-140","subject":"demo quest","priority":"P2","status":"done","updated_at":"2026-04-21T16:44:27.428124Z"},"Unblocked":null}}

Dependency

Stacks on PR #5 (feat/quest-fulfill) — quest_clear as a backward-compat alias only exists in that branch. Must be merged after PR #5.

Closes QUEST-138 · Spec: LORE-122 · Rename context: LORE-80