architecture: establish Codectx ambient HUD direction

[greygoody]

Purpose

Define Codectx as an always-present contextual HUD while preserving the current repository context compiler as its first repository lens.

Define the Codectx App as the host integration used by Orb, Codex, or another runtime to manage compositor lifecycle, lens wiring, subscriptions, projection delivery, and explicit moves.

Changes

• update the top-level identity;
• add the canonical HUD direction;
• add the Codectx App boundary;
• preserve ContextPacket v1 as the repository-lens contract;
• distinguish implemented behavior from future compositor and runtime work.

Compatibility

No Rust, crate, CLI, packet schema, focus behavior, Runseal boundary, legacy protocol, or Orb manifest changes are included.

Migration

1. Identity without behavior change.
2. Additive compositor and lens seams.
3. Runtime-hosted ambient projection proof.

[greygoody]

Step 1 verification

The branch is based on current main, is mergeable, and is 17 commits ahead with zero commits behind. The final diff is limited to five Markdown files:

README.md
docs/codectx-app-v0.md
docs/codectx-hud-v0/README.md
docs/context-packet-v1.md
docs/implementation-status.md

The proof workflow completed successfully for head 0700380edc47a9e7b837a0088b02fa8b6396d83f.

No Rust, crate layout, CLI behavior, packet schema, focus semantics, legacy protocol, Runseal authority, or Orb manifest changes are present.