[FLINK-39529][table] Add SQL-to-operator lifecycle and restructure planner AGENTS.md

[gustavodemorais]

What is the purpose of the change

As recently discussed in the mailing list, we want to work towards have more extensive and high quality Agents.md context files to make the codebase work better with AI. In that sense, we want to add a more detailed sql to operator lifecycle section to help AI tools to navigate the codebase.

Brief change log

• Add detailed sql to operator lifecycle
• Restructure Agents.md for future common tasks to be added

Verifying this change

• Review the information
• Fact check

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (Agents.md)

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: [2.1.117 (Claude Code)

[gustavodemorais]

The focus was to add the lifecycle overview and restructure it a bit. I didn't attempt to try to go into detail into the existing common subtasks here "Plan serialization changes, Adding a planner optimization rule" and just moved them around.

[flinkbot]

CI report:

• b1d1ebd Azure: SUCCESS

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