🤖 Add Zathras agent and initialize Spire for reliquary

Scaffold .claude/spire/project.md with reliquary-specific facts,
create adept templates at docs/workpad/adepts/, build the Zathras
agent and skill (Spire's self-maintenance coordinator), and wire
/assistant as a local alias for spire:zathras.

.claude/skills/assistant/SKILL.md

@@ -0,0 +1,9 @@
+---
+name: assistant
+description: Start a Zathras session — Spire's self-maintenance coordinator for this repo.
+user-invocable: true
+---
+
+Invoke the `spire:zathras` skill. Pass through any arguments:
+
+/spire:zathras $ARGUMENTS

.claude/spire/project.md

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+---
+status: generated
+generated: 2026-09-21
+---
+# Project Knowledge — Reliquary
+
+Project-specific facts for the session coordinator and the athanor. This is
+the Spire plugin's own home — work here is work ON Spire.
+
+## This project
+
+- **Tome skill**: none — orient via direct file reads
+- **Workpad**: `docs/workpad/` — goals/, plans/, reports/, research/, designs/, journals/, specs/, adepts/
+- **Adepts**: Listed by `spire:adepts` at boot. Domain knowledge agents with persistent folders at `docs/workpad/adepts/<domain-slug>/`.
+- **Pinned agents** (prefer these over generic tiers):
+  <!-- None pinned in .claude/agents/ yet -->
+- **Verification commands**: `just --list` (minimal Justfile — `claude-rc` recipe only)
+- **Domain skills to route to subagents when relevant**:
+  - `gitea:*` — Gitea issue and PR management
+- **Conventions**:
+  - Gitmoji commit prefixes — see `docs/workpad/specs/commit-conventions.md`
+  - Custom `🤖` prefix for agent-file changes (CLAUDE.md, skills, agents)
+  - `🦇 BATMAN` for initial commits
+  - Marketplace repo — each plugin under `plugins/` is self-contained
+  - Working documents live in `docs/workpad/`
+
+## Spire structure
+
+This is the home repo. The plugin itself lives at `plugins/spire/`.
+
+- **Agents**: `plugins/spire/agents/` — igor, athanor, adept, researcher, scout, search, zathras
+- **Skills**: `plugins/spire/skills/` — adepts, curator, igor, implementation, init, knowledge, project, research, research-tree, svg, workpad, zathras
+- **Plugin config**: `plugins/spire/.claude-plugin/plugin.json`
+- **Design spec**: `docs/workpad/designs/2026-09-14-plugin-design-spec.md`
+- **Legacy**: `plugins/g4b_ai/` still exists (predecessor, being phased out)