Give every prompt one shared context block

The "address him as ты" rule had only reached two of the five system
prompts. Instead of pasting it into the other three (five copies drift —
that is how this happened), there is now one block, in internal/persona,
prepended to all five: nudges, action replies, chat, note queries and
general knowledge.

The block says who he is and how to address him (a man, always "ты",
never "вы", never "он" about him; Maven stays feminine), plus the
current local date and time. It is rendered fresh each turn because the
time changes, and it is correct with an empty config — the address and
gender rules are defaults in code. Config only adds optional facts:
owner_name, city, and the existing free-text `persona` string, which is
now the static half of the block.

Russian even in front of the English prompts: the rules are Russian
grammar, so they read best stated in Russian, and there is one copy.

Vikunja #394.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

internal/config/config.go

@@ -302,6 +302,13 @@ type VoiceConfig struct {
 	// Russian self-reference). Example: "Be formal and answer in English only."
 	Persona string `json:"persona,omitempty"`
 
+	// OwnerName / City — optional facts about the owner, added to the shared
+	// context block (internal/persona). Empty is fine: the block still states
+	// who he is grammatically (a man, addressed as "ты") and the current time.
+	// Nothing about correct behaviour may depend on these being filled in.
+	OwnerName string `json:"owner_name,omitempty"`
+	City      string `json:"city,omitempty"`
+
 	// Weather — the weather provider config. nil ⇒ the daemon wires
 	// the stub provider (returns ErrNotConfigured — "погода не настроена").
 	// Set provider to "open-meteo" to use the keyless Open-Meteo API.