refactor(settings): treat unset spellings of every optional string as None

Review follow-up. The per-group secret validators normalised a hand-picked
list of API keys, which left other optional credentials and overrides
(OPEN_ROUTER_API_KEY, S3 and Daytona keys, ELASTIC_PASSWORD, the OIDC
trio, connector client ids, MICROSOFT_AUTHORITY, MCP_OAUTH_REDIRECT_URI)
holding the literal "None" or "" a .env file spells "unset" with, so
truthiness checks and fallbacks downstream saw a value. One rule on the
group base replaces those lists: every Optional[str] field maps "", "None"
and whitespace to None and strips real values. Plain str fields are left
alone. The OIDC required-settings check therefore also rejects those
spellings.

EMBEDDINGS_POOLING is Literal["cls", "mean"] with case-insensitive
parsing; its consumer silently ignored anything else.

Bounds added where the consumer rejects or misbehaves on the value:
SCHEDULE_RUN_OUTPUT_RETENTION_DAYS and MESSAGE_EVENTS_RETENTION_DAYS (the
cleanup repositories raise on <= 0), EMBEDDINGS_DELEGATE_TIMEOUT, the
remote-device idle/pairing/invocation TTLs and CELERY_VISIBILITY_TIMEOUT
(> 0), REMOTE_DEVICE_CMD_QUEUE_TTL_SECONDS (> 605, the documented drain
deadline), GRAPHRAG_MAX_CHUNKS_FOR_EXTRACTION (>= 0; negative would slice
the pending list from the end).

The generated reference now renders generic type arguments
(dict[str, int] rather than dict).

docsgpt/core/settings/embeddings.py

@@ -2,12 +2,12 @@
 
 from __future__ import annotations
 
-from typing import Optional
+from typing import Literal, Optional
 
 from pydantic import Field, field_validator
 
 from docsgpt.core.paths import home_dir
-from docsgpt.core.settings._shared import SettingsGroup, normalize_secret
+from docsgpt.core.settings._shared import SettingsGroup, normalize_choice
 
 
 class EmbeddingsSettings(SettingsGroup):
@@ -56,7 +56,7 @@ class EmbeddingsSettings(SettingsGroup):
             "default is the temp dir."
         ),
     )
-    EMBEDDINGS_POOLING: Optional[str] = Field(
+    EMBEDDINGS_POOLING: Optional[Literal["cls", "mean"]] = Field(
         default=None,
         description=(
             'Pooling strategy ("cls" or "mean"). Read from the model\'s own repository; set only for a '
@@ -79,10 +79,10 @@ class EmbeddingsSettings(SettingsGroup):
     )
     EMBEDDINGS_QUEUE: str = Field(default="embeddings", description="Celery queue the embed task is routed to.")
     EMBEDDINGS_DELEGATE_TIMEOUT: int = Field(
-        default=60, description="Seconds the API waits for the worker to return an embedding."
+        default=60, gt=0, description="Seconds the API waits for the worker to return an embedding."
     )
 
-    @field_validator("EMBEDDINGS_KEY", mode="before")
+    @field_validator("EMBEDDINGS_POOLING", mode="before")
     @classmethod
-    def _normalize_embeddings_secrets(cls, v):
-        return normalize_secret(v)
+    def _normalize_pooling(cls, v):
+        return normalize_choice(v)