feat(Feature Lifecycle): Update API with feature lifecycle info

[emyller]

• I have read the Contributing Guide.
• I have added information to docs/ if required so people know about the feature.
• I have filled in the "Changes" section below.
• I have filled in the "How did you test this code" section below.

Changes

Closes #7433

1. Introduces a new endpoint (also to MCP) /api/v1/environments/{environment}/feature-lifecycle-counts/

   {
     "NEW": 475,
     "LIVE": 734,
     "PERMANENT": 190,
     "STALE": 374,
     "NEEDS_MONITORING": 30,
     "TO_REMOVE": 197
   }

2. Adds new query params to the existing GET /api/v1/projects/{project_pk}/features/ (list):
   • lifecycle_stage: one of stages below; requires environment.
3. Adds a new attribute lifecycle_stage to the above list endpoint, and also to .../{feature_id} (retrieve), also carrying one of stages below.

Stages logical propositions are as follows:

State	Condition
PERMANENT	has_permanent_tag
LIVE	~has_permanent_tag AND ~has_stale_tag AND has_code_references
NEW	~has_permanent_tag AND ~has_stale_tag AND ~has_code_references
STALE	~has_permanent_tag AND has_stale_tag AND has_code_references
NEEDS_MONITORING	~has_permanent_tag AND has_stale_tag AND ~has_code_references AND evaluated_recently
TO_REMOVE	~has_permanent_tag AND has_stale_tag AND ~has_code_references AND ~evaluated_recently

How did you test this code?

• New tests
• Will gradually roll out in production and collect perf data
• LLM-assisted benchmarking (does not represent production):

method: synthetic data, InfluxDB analytics backend, local Docker (indicative)
baseline: main's list/detail query path (already annotates code-refs), no lifecycle

small_project:        # 1K flags, 200 in use
  influxdb_query: ~80ms
  feature_list:
    baseline_main: ~2ms
    pr_no_stage_filter: ~40ms
    pr_filtered_by_stage: ~85ms
  feature_detail:
    baseline_main: ~1ms
    pr_with_lifecycle: ~35ms
  stage_counts_endpoint: ~55ms   # new in PR, no baseline

stress_test:          # 30K flags, 600 in use — deliberate worst-case
  influxdb_query: ~120ms
  feature_list:
    baseline_main: ~8ms
    pr_no_stage_filter: ~0.12s
    pr_filtered_by_stage: ~0.45s
  feature_detail:
    baseline_main: ~1ms
    pr_with_lifecycle: ~70ms
  stage_counts_endpoint: ~0.35s

How to review

Reviewing is easier if you split:

• Part 1: InfluxDB API refactor (to enable tests) — it revealed we need to rewrite it, or maybe invest in something else.
• Part 2: Feature Lifecycle stage counts API (to feed the count badges in the sidebar.
• Part 3: Extend the feature list and retrieve endpoints with lifecycle stage information.
• Part 4: Add filter by lifecycle stage capability to the feature list endpoint.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview, Comment	Jun 24, 2026 8:07pm

2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
flagsmith-frontend-preview	Ignored	Preview	Jun 24, 2026 8:07pm
flagsmith-frontend-staging	Ignored	Preview	Jun 24, 2026 8:07pm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.61%. Comparing base (d991940) to head (019b529).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7789      +/-   ##
==========================================
+ Coverage   98.59%   98.61%   +0.01%     
==========================================
  Files        1472     1481       +9     
  Lines       57370    58068     +698     
==========================================
+ Hits        56564    57262     +698     
  Misses        806      806              

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