docs: remove model-specific references from documentation

[Copilot]

Description

Remove model-specific documentation (CESM namelist URLs, CESM-ECT branding, cheyenne machine references, CESM-specific paths) while preserving model references that provide useful context for users.

Removed (not directly relevant to CIME):

• CESM-specific active component namelist section in setting-up-a-case.rst (CAM, CLM, CICE, POP2, CISM with cesm.ucar.edu URLs) — replaced with generic component namelist guidance
• CESM-ECT branding/paths/URLs in tools/ect.rst and support-a-new-machine.rst
• Cheyenne-specific test commands and paths throughout
• CESM-specific path examples (/glade/scratch/cesm_user, $CESMDATAROOT)

Generalized (relevant to CIME, made model-agnostic):

• Docker examples in contributing-guide.rst → <model> placeholders
• Test output paths in system_testing.rst
• Grid config paths in grids.rst
• "CESM executable" → "model executable" in running-a-case.rst
• "CAM and CLM history files" → "component history files" in troubleshooting.rst
• Added context notes to model-specific example outputs (timers, preview_run)

Kept (provides useful context):

• E3SM/CESM project links in footer, prerequisites, CIME_MODEL possibilities
• Compset examples with model attribution, historical convention notes
• XML config examples showing real values (cime_model="cesm")

Also fixes pre-existing typo: tempororal → temporal in pes.rst.

Checklist

• My code follows the style guidelines of this project (black formatting)
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have added tests that exercise my feature/fix and existing tests continue to pass
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding additions and changes to the documentation