feat(config): centralise all config via pydantic-settings env loader (#32)

[ArokyaMatthew]

Summary

Closes #32

Centralises all scattered configuration (hardcoded constants, inline thresholds, .env.example drift) into a single pydantic-settings BaseSettings class at libs/config/settings.py.

Problem

The existing settings.py had critical bugs:

• lingering_threshold_sec, movement_threshold_px, near_keypad_dist_px, keypad_center_x, keypad_center_y were declared three times with conflicting defaults (5.0/10.0, 10.0/15.0/5.0, etc.) — only the last declaration wins in Python, silently overriding earlier values
• max_events_per_track (50) was hardcoded in memory.py and ring_buffer.py with no env override
• track_ttl_seconds (86400) was hardcoded in memory.py and action_bridge.py with no env override
• .env.example was missing most settings fields

Changes

libs/config/settings.py

• Deduplicated all fields — each appears exactly once with the correct default from the issue spec
• Added max_events_per_track: int = 50 and track_ttl_seconds: int = 86_400
• Organised fields into logical groups (Redis, Memory, Action classifier, Detection, Tracker, VLM/LLM, Reasoning, Backend, Kafka)

services/memory/memory.py

• TRACK_TTL_SECONDS and EVENT_TTL_SECONDS now read from settings.track_ttl_seconds
• MAX_EVENTS_PER_TRACK now reads from settings.max_events_per_track

services/memory/ring_buffer.py

• MAX_EVENTS_PER_TRACK now reads from settings.max_events_per_track

services/memory/action_bridge.py

• TRACK_TTL_SECONDS now reads from settings.track_ttl_seconds

.env.example

• Expanded to document all settings fields with their defaults, grouped by category

tests/test_settings.py (new — 26 tests)

Class	Tests	Coverage
TestDefaults	13	Verifies every default matches the issue's contract
TestEnvOverrides	11	Uses monkeypatch.setenv() to verify env vars override defaults
TestSingleton	2	Verifies the module-level settings instance is importable and valid

Acceptance Criteria Checklist

• Remove hardcoded thresholds from production code
• Use centralised settings
• .env.example updated
• Environment overrides tested (11 override tests with monkeypatch)
• Existing tests remain green

Test Results

tests/test_settings.py — 26 passed
tests/test_reasoning_fixtures.py — 4 passed
tests/test_policy_loader.py — 2 passed

Screenshots

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Configuration used: defaults

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📥 Commits

Reviewing files that changed from the base of the PR and between 8de0807 and dd09107.

📒 Files selected for processing (6)

• .env.example
• libs/config/settings.py
• services/memory/action_bridge.py
• services/memory/memory.py
• services/memory/ring_buffer.py
• tests/test_settings.py

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