docs(plans): add Agent Hub 22-agent enablement spec (#1457)

## Why this matters

GAIA's roadmap names ~22 purpose-built agents (email, smart home,
knowledge, finance, etc.) but had no single plan for *how* to build and
ship them consistently. This spec closes that gap: it defines a
repeatable model so each agent is a thin, Hub-native package over shared
infrastructure — not 22 bespoke codebases. The payoff is that adding an
agent becomes ~150–500 LOC of glue plus a manifest, and every agent
ships with the same packaging, autonomy, and personalization guarantees.

The spec turns "we want these agents" into an executable, waved plan
with a concrete issue breakdown.

## What's in it

- **Two-layer model** — 7 shared infrastructure layers (memory, web
search, connectors, VLM/media, filesystem, notifications, autonomy) + 22
thin agent packages.
- **5-interface packaging standard** — every agent is one compiled
package exposing TUI / CLI / pipe / API server (+OpenAPI) / MCP server,
published to R2 and surfaced on the website + Agent UI. Python now, C++
supersession path that keeps id/manifest/interfaces unchanged.
- **Autonomy Model** — default posture (observe/prepare autonomous,
commit gated), trigger taxonomy, the autonomous loop, graduated trust,
and a per-agent user journey from install to steady state.
- **Personalization Model** — memory-vs-datastore architecture,
explicit/implicit/bootstrap capture, scoped retrieval, the
cold-start→personalized lifecycle, privacy/control, and a per-agent
personalization table.
- **Waved sequencing + full issue breakdown** (§9), with memory tier
(essential/enhance/optional) and datastore type per agent.

## Test plan

- [ ] Render-check the Markdown (tables, code fences, section numbering
1–12 sequential).
- [ ] Confirm no dangling internal references (the companion issues doc
/ strategic analysis are intentionally not in this PR).
- [ ] Maintainer review of the layer/wave sequencing and the per-agent
autonomy + personalization tables.

Scope note: this PR adds the spec only
(`docs/plans/agent-hub-22-agents-spec.md`). The companion issue-set doc
and the milestone/issues are handled separately.

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Co-authored-by: Ovtcharov <kovtchar@amd.com>

Author: kovtcharov-amd