Docs: add early-alpha warning to landing page

[EiffL]

Adds an early-alpha admonition to the docs landing page, mirroring the one on the ASTRA spec site: breaking changes expected between minor versions, and a pointer to the issue tracker for bug reports and design feedback.

The docs have already been redeployed from this branch via workflow_dispatch (no release/version change); merging keeps the warning in place for future release-triggered deploys.

🤖 Generated with Claude Code

https://claude.ai/code/session_018RdnNAzntq6EYuJw9rGNQf

[github-actions]

❌ Eval Results

Metric	Value
Score	0.00
Build complete	❌
Cost	$0.00
Turns	0
Duration	0s
lightcone-cli	0.4.2.dev2+g49559637d (49559637)
Results	Download

Graders

No grader results

Full output

13:10:40 lightcone.eval.build Building lightcone-cli wheel from /home/runner/work/lightcone-cli/lightcone-cli ...
13:10:45 lightcone.eval.build Built lightcone_cli-0.4.2.dev2+g49559637d-py3-none-any.whl (commit 49559637)
13:10:48 lightcone.eval.harness Trial build-snae-0 failed: Authentication credentials not found. Set DAYTONA_API_KEY, or both DAYTONA_JWT_TOKEN and DAYTONA_ORGANIZATION_ID. These can also be provided via DaytonaConfig.
Traceback (most recent call last):
  File "/home/runner/work/lightcone-cli/lightcone-cli/src/lightcone/eval/harness.py", line 112, in run_trial
    sandbox.create()
  File "/home/runner/work/lightcone-cli/lightcone-cli/src/lightcone/eval/sandbox.py", line 70, in create
    self._daytona = Daytona()
                    ^^^^^^^^^
  File "/home/runner/work/lightcone-cli/lightcone-cli/.venv/lib/python3.12/site-packages/daytona_sdk/_sync/daytona.py", line 186, in __init__
    raise DaytonaAuthenticationError(msg)
daytona_sdk.common.errors.DaytonaAuthenticationError: Authentication credentials not found. Set DAYTONA_API_KEY, or both DAYTONA_JWT_TOKEN and DAYTONA_ORGANIZATION_ID. These can also be provided via DaytonaConfig.
  snae trial 0: score=0.00 error: Authentication credentials not found. Set 
DAYTONA_API_KEY, o

lightcone-cli: 0.4.2.dev2+g49559637d (HEAD 49559637)
ASTRA: 0.2.11

  Eval Results: Scores  
┏━━━━━━┳━━━━━━━━━━━━━━━┓
┃ Task ┃     Score     ┃
┡━━━━━━╇━━━━━━━━━━━━━━━┩
│ snae │ 0.00 +/- 0.00 │
│      │  pass@k: 0%   │
│      │   1 errors    │
└──────┴───────────────┘

   Eval Results: Cost &   
         Duration         
┏━━━━━━┳━━━━━━━━━━━━━━━━━┓
┃ Task ┃ Cost / Duration ┃
┡━━━━━━╇━━━━━━━━━━━━━━━━━┩
│ snae │      $0.00      │
│      │       0s        │
└──────┴─────────────────┘

Total: 1 trials, $0.00, 0s

Results saved to: eval-results/build-49559637/results.json