fix(coding-agent): identify user-invoked skills and expose skill directory

User-invoked skills (typed /skill:, steered, follow-up, interrupted/
resumed via compaction, ACP, RPC) only appended a bare "Skill: <path>"
line, so the model neither learned the user had invoked that specific
skill nor where the skill directory was. Relative paths in skill bodies
(scripts/, templates/) could not be resolved.

Route all user-invoked paths through a self-identifying, baseDir-aware
prompt template; keep hidden autoload skills on the minimal non-user
format. Interactive skillCommands now carries the loaded Skill object
instead of a bare path so baseDir flows through without reconstruction.
The invocation kind defaults to "user" to keep buildSkillPromptMessage
source-compatible.

Op: correct
Restores: spec:user-invoked-skill-prompt-self-identifies-and-exposes-skill-directory

packages/coding-agent/src/modes/controllers/command-controller.ts

@@ -1160,21 +1160,6 @@ export class CommandController {
 		this.ctx.showStatus(formatShakeSummary(result));
 	}
 
-	async handleSkillCommand(skillPath: string, args: string): Promise<void> {
-		try {
-			const content = await Bun.file(skillPath).text();
-			const body = content.replace(/^---\n[\s\S]*?\n---\n/, "").trim();
-			const metaLines = [`Skill: ${skillPath}`];
-			if (args) {
-				metaLines.push(`User: ${args}`);
-			}
-			const message = `${body}\n\n---\n\n${metaLines.join("\n")}`;
-			await this.ctx.session.prompt(message);
-		} catch (err) {
-			this.ctx.showError(`Failed to load skill: ${err instanceof Error ? err.message : String(err)}`);
-		}
-	}
-
 	async executeCompaction(
 		customInstructionsOrOptions?: string | CompactOptions,
 		isAuto = false,