Fix TOML encoder to quote keys containing special characters

[Copilot]

TOML bare keys are restricted to [A-Za-z0-9_-]. The encoder was emitting keys like http://sealos.hub:5000 or /tmp/blah unquoted, producing invalid TOML that failed to re-parse.

Changes

• encoder_toml.go: Added two helpers:
  • tomlKey(key) — returns key unchanged if it's a valid bare key, otherwise wraps it with %q
  • tomlDottedKey(path) — joins path segments for table/array-of-tables headers, quoting each segment as needed
• Applied these helpers across all key-emission sites: scalar attributes, array attributes, inline table keys, [[array-of-tables]] headers, and [table] section headers

Example

Before (invalid TOML):

host = { http://sealos.hub:5000 = { capabilities = ["pull", "resolve", "push"], skip_verify = true } }

After (valid, re-parseable TOML):

host = { "http://sealos.hub:5000" = { capabilities = ["pull", "resolve", "push"], skip_verify = true } }