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.

src/everos/core/errors.py

@@ -0,0 +1,33 @@
+"""Cross-cutting domain errors surfaced to API callers.
+
+These live in ``core`` so the ``memory`` layer can raise them and the
+``entrypoints`` layer can catch them without crossing the layered import
+boundary — ``any -> core`` is the only edge both share (entrypoints must
+not import ``memory`` directly).
+"""
+
+from __future__ import annotations
+
+
+class MultimodalError(Exception):
+    """Base for multimodal-parsing errors meant to reach the caller.
+
+    The API layer maps any ``MultimodalError`` to an aligned
+    ``{error: {code, message}}`` envelope (HTTP 415).
+    """
+
+
+class UnsupportedModalityError(MultimodalError):
+    """everalgo cannot handle this modality (e.g. video stub, unknown type).
+
+    Wraps everalgo's ``NotImplementedError`` / dispatch ``ValueError`` so the
+    caller gets a stable, aligned error instead of a raw 500.
+    """
+
+
+class MultimodalNotEnabledError(MultimodalError):
+    """Multimodal capability is not ready.
+
+    Raised when the ``everos[multimodal]`` extra is not installed, or when a
+    required system dependency (LibreOffice for Office documents) is absent.
+    """