feat(hindsight): default recall_types to observation only

Auto-recall used to surface every fact type Hindsight had on the
session — `world`, `experience`, and `observation`. That triple-ships
the same underlying signal in three different framings: observations
are the concrete events the user said/did/asked, while world and
experience facts are aggregate summaries Hindsight derives from those
exact observations. Including all three burns most of
`recall_max_tokens` on rephrasings, crowds out events the model
actually needs to see, and produces effective duplicates in the
prompt — observations themselves are deduplicated by construction
so observation-only recall is denser per token and closer to
conversational ground truth.

Change
------
- Default `_recall_types = ["observation"]` (was `None`, which
  delegated to server-side "return everything").
- `initialize()` now treats a missing `recall_types` config the same
  way; also accepts comma-separated strings for parity with `recall_tags`.
- An explicit `recall_types=[]` config falls back to the default rather
  than disabling the filter (would silently widen recall vs. the new
  default).
- Added to `get_config_schema()` so it's discoverable via `hermes config`.

Per-call `hindsight_recall` tool invocations are unaffected — they
already only forward `types` when the caller passes the argument.

Docs / migration
----------------
plugins/memory/hindsight/README.md grows a "Behavior change" callout
explaining the why (no-duplicates, information-efficient) and how to
restore the legacy broad recall:

    "recall_types": "observation,world,experience"   # or a JSON list

in `~/.hermes/hindsight/config.json`.

Tests
-----
- `test_default_values` updated for the new default.
- New cases: explicit list override, CSV string accepted, empty list
  falls back to default (not "wider than default").

plugins/memory/hindsight/README.md

@@ -75,8 +75,17 @@ Config file: `~/.hermes/hindsight/config.json`
 | `recall_prompt_preamble` | — | Custom preamble for recalled memories in context |
 | `recall_tags` | — | Tags to filter when searching memories |
 | `recall_tags_match` | `any` | Tag matching mode: `any` / `all` / `any_strict` / `all_strict` |
+| `recall_types` | `observation` | Fact types surfaced by auto-recall. Comma-separated string or JSON list. **Default narrowed to `observation` only** (see "Behavior change" below). Set to `observation,world,experience` to also include raw facts. |
 | `auto_recall` | `true` | Automatically recall memories before each turn |
 
+> **Behavior change — `recall_types` defaults to `observation` only.**
+>
+> Previously auto-recall returned all three fact types. It now returns only observations.
+>
+> Per [Hindsight's docs](https://hindsight.vectorize.io/developer/observations), observations are the **consolidated** knowledge layer Hindsight builds on top of raw facts: deduplicated beliefs grounded in evidence, refined as new facts arrive, with proof counts and freshness signals. Raw `world` / `experience` facts are the individual supporting evidence that feeds them. For per-turn context injection, observations are denser per token and avoid feeding the model multiple raw facts that one observation already summarizes.
+>
+> Restore the broad recall with `"recall_types": "observation,world,experience"` (string or JSON list) in `~/.hermes/hindsight/config.json`. Per-turn `hindsight_recall` tool calls are unaffected — they only filter by `types` when the tool argument is passed explicitly.
+
 ### Retain
 
 | Key | Default | Description |