feat(vocero): add linked content and TALKFIRST greetings (#2)

Opening a report or podcast link now establishes an authenticated starting reference for the conversation. Users can select other accessible content or compare reports while retaining the original link, and TALKFIRST greetings can name the verified report or podcast.

Release notes:

- Added authenticated report and episode link resolution with bounded lookups and unavailable-content handling
- Added explicit conversation selection without restricting searches or changing the reference during comparisons
- Added contextual TALKFIRST greetings through both voice-proxy and HTTP reasoning paths
- Preserved backend permission checks, conversation isolation, cancellation, and the existing speech protocol

Reviewed-on: AquaPortal/s2s#2

vocero-api/vocero_api/models/content.py

@@ -0,0 +1,43 @@
+"""Compact, immutable references returned by authenticated content lookups."""
+
+from datetime import date
+from typing import Annotated, Literal
+
+from pydantic import BaseModel, ConfigDict, Field, StringConstraints
+
+ContentId = Annotated[str, StringConstraints(strip_whitespace=True, min_length=1, max_length=200)]
+PodcastId = Annotated[str, StringConstraints(pattern=r"^(daily|report):\S.{0,199}$")]
+
+
+class ContentReference(BaseModel):
+    model_config = ConfigDict(frozen=True)
+    id: ContentId
+    title: str = Field(min_length=1, max_length=2000)
+    date: date
+
+
+class ReportReference(ContentReference):
+    has_podcast: bool
+
+
+class PodcastReference(ContentReference):
+    id: PodcastId
+    kind: Literal["daily", "report"]
+
+
+class ConversationContent(BaseModel):
+    model_config = ConfigDict(frozen=True)
+    report: ReportReference | None = None
+    podcast: PodcastReference | None = None
+    unavailable: bool = False
+
+
+class ContentSelection(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    kind: Literal["report", "podcast"]
+    id: Annotated[str, StringConstraints(strip_whitespace=True, min_length=1, max_length=207)]
+
+
+class SelectContentRequest(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+    request: ContentSelection