chore: initialize EverOS 1.0.0

md-first memory extraction framework for AI agents.

Markdown is the single source of truth; SQLite holds state and LanceDB
provides the rebuildable vector + BM25 + scalar index. The codebase follows
a single-direction DDD layering (entrypoints -> service -> memory -> infra,
with component / core / config cross-cutting) enforced by import-linter.

Engineering surface:
- Coding conventions in .claude/rules/ (path-scoped) and workflows in
  .claude/skills/ (/commit, /new-branch, /pr).
- GitHub Actions CI runs make lint + test + integration; pre-commit mirrors
  the gates locally (ruff, hygiene hooks, gitlint commit-msg).
- Commit messages follow Conventional Commits, enforced by gitlint.
- make lint also enforces datetime two-zone discipline and OpenAPI drift.

docs/prompt_slots.md

@@ -0,0 +1,111 @@
+# PromptSlot
+
+PromptSlot is the layer between the algorithm code (`everalgo`) and
+the prompts it sends to LLMs. Algorithm code receives a `PromptSlot`
+parameter; the *project* (EverOS) supplies defaults and lets operators
+override.
+
+> **Status (2026-05-07)**: the YAML loader is implemented; the higher-
+> level `PromptSlot` model + sandbox dry-run + three-layer overlay
+> resolution arrive when the memory layer ships (see Stage 2).
+
+## Three-layer overlay
+
+```
+config/prompt_slots/<name>.yaml          (Layer 1: defaults shipped with the package)
+       ↓
+~/.everos/prompt_slots/<name>.yaml       (Layer 2: app-level override; per-deployment)
+       ↓
+runtime override                         (Layer 3: per-call override; e.g. "force model X")
+```
+
+Effective prompt = layer 3 wins → layer 2 → layer 1. Layer 1 is
+loaded eagerly at startup; layer 2 is loaded on first reference (lazy);
+layer 3 is supplied at the call site.
+
+## Loader
+
+The category loader lives at
+[`src/everos/component/config/loader.py`](../src/everos/component/config/loader.py)
+as `YamlConfigLoader`:
+
+```python
+from pathlib import Path
+from everos.component.config import YamlConfigLoader
+
+loader = YamlConfigLoader(
+    root=Path("src/everos/config"),
+    categories={"prompt_slots": None},   # subdir == category name
+)
+
+# Reads <root>/prompt_slots/episode_extract.yaml → dict
+slot = loader.find("prompt_slots", "episode_extract")
+
+# Refresh after on-disk edits.
+loader.refresh()                         # drop the entire cache
+loader.refresh("prompt_slots")           # drop one category
+loader.refresh("prompt_slots", "episode_extract")  # drop one entry
+```
+
+Top-level YAML is required to be a mapping; a list / scalar root
+raises `TypeError` to fail-fast (loud, not silent).
+
+## YAML format (proposed; subject to change)
+
+```yaml
+# config/prompt_slots/episode_extract.yaml
+template: |
+  Extract a single episode from this conversation:
+  {{ memcell.text }}
+
+variables:
+  memcell: input memcell
+
+output_schema:
+  type: object
+  properties:
+    summary: { type: string }
+    participants: { type: array }
+
+llm:
+  model: gpt-4o-mini
+  temperature: 0.3
+  max_tokens: 2000
+
+validation:
+  test_cases:
+    - input: { memcell: { text: "Hi" } }
+      expected: { summary: "...", participants: [] }
+```
+
+When layer 2 supplies an override the loader will be re-pointed at
+`~/.everos/prompt_slots/`; the runtime resolution logic (currently TBD)
+sandbox-runs the merged slot before returning it.
+
+## Why YAML (not TOML)
+
+Two reasons:
+
+1. **Multiline templates** — TOML's basic-string grammar fights
+   prompt content (no easy `{{ jinja }}` variables, awkward escaping).
+   YAML's literal block scalar (`|`) preserves prompts as-is.
+2. **Comment + reference ergonomics** — operators frequently inherit
+   slots, tweak a few keys, and leave inline notes. YAML is more
+   forgiving for hand-editing.
+
+The Pydantic Settings file (`config/default.toml`) stays TOML — it's
+machine-managed and type-validated; YAML's flexibility costs more
+than it pays for that case.
+
+## Why a separate loader (not Pydantic Settings)
+
+Settings = **one** structured tree, validated at load time, tied to a
+single source of truth. PromptSlots = **many** separate templates
+discovered by name, layered per-deployment. They're different shapes;
+forcing one model on the other gets clunky.
+
+## See also
+
+- [`src/everos/component/config/loader.py`](../src/everos/component/config/loader.py)
+- [`tests/unit/test_component/test_config/test_loader.py`](../tests/unit/test_component/test_config/test_loader.py)
+- [`docs/architecture.md`](architecture.md) — layer placement